Preview Cambridge IGCSE Combined and Co-ordinated Sciences Physics Workbook by Cambridge International Education

This physics workbook is tailored to the Cambridge IGCSE Combined Science (0653) and Cambridge IGCSE Co-ordinated Sciences (0654) syllabuses for first examination in 2019, and is endorsed for learner support by Cambridge International Examinations.

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Combined and Co-ordinated Sciences

The workbook: • Focuses on the skills students need for scientific study, including problem-solving, handling, interpreting and presenting data, as well as investigating and experimenting. • Contains exercises that are arranged in the same order as the chapters in the Physics section of the coursebook, and are clearly marked according to the syllabus they cover. • Is written in a clear and accessible style with the international learner in mind.

Cambridge IGCSE®

Cambridge IGCSE® Combined and Co-ordinated Sciences Physics Workbook David Sang

David Sang

Cambridge IGCSE®

Combined and Co-ordinated Sciences Physics Workbook

Physics Workbook

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Original material © Cambridge University Press 2017

David Sang

Cambridge IGCSEÂŽ

Combined and Co-ordinated Sciences Physics Workbook

Original material ÂŠ Cambridge University Press 2017

University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 4843/24, 2nd Floor, Ansari Road, Daryaganj, Delhi – 110002, India 79 Anson Road, #06–04/06, Singapore 079906 Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781316631065 © Cambridge University Press 2017 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2017 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Printed in Malaysia by Vivar Printing A catalogue record for this publication is available from the British Library ISBN 978-1-316-63106-5 Paperback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. NOTICE TO TEACHERS IN THE UK It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the Copyright Licensing Agency; (ii) where no such licence exists, or where you wish to exceed the terms of a license, and you have gained the written permission of Cambridge University Press; (iii) where you are allowed to reproduce without permission under the provisions of Chapter 3 of the Copyright, Designs and Patents Act 1988, which covers, for example, the reproduction of short passages within certain types of educational anthology and reproduction for the purposes of setting examination questions.

® IGCSE is the registered trademark of Cambridge International Examinations. Example answers and all questions were written by the author.

Original material © Cambridge University Press 2017

Contents Introduction v

P7 Energy resources

P7.01 Renewables and non-renewables

P7.02 Wind energy

P7.03 Energy from the Sun

P1 Making measurements

P1.01 The SI system of units

P1.02 Accurate measurements

P1.03 Density data

P8 Work and power

P1.04 Testing your body clock

P8.01 Forces doing work, transferring energy

P2 Describing motion

P8.02 Calculating work done

P2.01 Measuring speed

P8.03 Measuring work done

P2.02 Speed calculations

P8.04 Power

P2.03 More speed calculations

P9 The kinetic model of matter

P2.04 Distance–time graphs

P9.01 Changes of state

P2.05 Acceleration

P9.02 The kinetic model of matter

P2.06 Speed–time graphs

P9.03 Brownian motion

P3 Forces and motion

P9.04 Understanding gases

P3.01 Identifying forces

P10 Thermal properties of matter

P3.02 The effects of forces

P10.01 Demonstrating thermal expansion

P3.03 Combining forces

P10.02 Thermal expansion

P3.04 Mass and weight

P10.03 Energy and temperature

P3.05 Force, mass and acceleration

P10.04 Calibrating a thermometer

P4 Turning effects of forces

P4.01 Turning effect of a force

P11 Thermal (heat) energy transfers 57

P4.02 Calculating moments

P4.03 Stability and centre of mass

P4.04 Make a mobile

P5 Forces and matter

P5.01 Stretching a spring

P5.02 Stretching rubber

P5.03 Pressure

P11.01 Conductors of heat

P11.02 Convection currents

P11.03 Radiation

P11.04 Losing heat

P11.05 Warming up, cooling down

P12 Sound

P12.01 Sound on the move

P6 Energy transformations and energy transfers

P12.02 Sound as a wave

P13 Light

P6.01 Recognising forms of energy

P13.01 On reflection

P6.02 Energy efficiency

P13.02 Refraction of light

P6.03 Energy calculations

P13.03 The changing speed of light 35 Original material © Cambridge University Press 2017

iii

Cambridge IGCSE Combined and Co-ordinated Sciences

P13.04 A perfect mirror

P19 Electric circuits

P13.05 Image in a lens

P19.01 Circuit components and their symbols

P14 Properties of waves

P19.02 Resistor combinations

100

P14.01 Describing waves

P19.03 More resistor combinations

102

P14.02 The speed of waves

P19.04 Electrical safety

104

P14.03 Wave phenomena

P20 Electromagnetic forces

P15 Spectra

P20.01 Using electromagnetism

P15.01 Electromagnetic waves

P21 Electromagnetic induction

P15.02 Using electromagnetic radiation

P21.01 Electricity generation

108

P16 Magnetism

P21.02 Transformers

109

P16.01 Attraction and repulsion

P22 The nuclear atom

P16.02 Magnetic fields

P22.01 The structure of the atom

113

P17 Electric charge

P22.02 Isotopes

114

P17.01 Attraction and repulsion

P22.03 The nature of radiation

115

P17.02 Static at home

P22.04 Radioactive decay equations

116

P18 Electrical quantities

P22.05 Radioactive decay

118

P22.06 Using radioactive substances

121

P18.01 Current in a circuit

P18.02 Current and charge

P18.03 Electrical resistance

P18.04 Current–voltage characteristics

P18.05 Electrical energy and power

106 106

108

112

Answers 122

Original material © Cambridge University Press 2017

Introduction This workbook covers two syllabuses: Cambridge IGCSE Combined Science (0653) and Cambridge IGCSE Co-ordinated Sciences (0654). Before you start using this workbook, check with your teacher which syllabus you are studying and which papers you will take. You will sit either the Core paper or the Extended paper for your syllabus. If you are sitting the Extended paper, you will study the Core material and the Supplement material for your syllabus. Once you know which paper you will be sitting, you can use the exercises in this workbook to help develop the skills you need and prepare for your examination. The examination tests three different Assessment Objectives, or AOs for short. These are: AO1 Knowledge with understanding AO2 Handling information and problem solving AO3 Experimental skills and investigations. In the examination, about 50% of the marks are for AO1, 30% for AO2 and 20% for AO3. Just learning your work and remembering it is therefore not enough to make sure that you get the best possible grade in the exam. Half of all the marks are for AO2 and AO3. You need to be able to use what you’ve learned in unfamiliar contexts (AO2) and to demonstrate your experimental skills (AO3). There are lots of activities in your coursebook which will help you to develop your experimental skills by doing practical work. This workbook contains exercises to help you to develop AO2 and AO3 further. There are some questions that just involve remembering things you have been taught (AO1), but most of the questions require you to use what you’ve learned to work out, for example, what a set of data means, or to suggest how an experiment might be improved.

These exercises are not intended to be exactly like the questions you will get on your exam papers. This is because they are meant to help you to develop your skills, rather than testing you on them. There’s an introduction at the start of each exercise that tells you the purpose of it – which skills you will be working with as you answer the questions. There are sidebars in the margins of the book to show which material relates to each syllabus and paper. If there is no sidebar, it means that everyone will study this material.

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

Use this table to ensure that you study the right material for your syllabus and paper:

Cambridge IGCSE Combined Science (0653)

Cambridge IGCSE Co-ordinated Sciences (0654)

Core

Supplement

Core

Supplement

You will study the material:

Without a sidebar

You will study everything. This includes the material:

With a double grey sidebar

With a single grey sidebar

With a double black sidebar

With a double grey sidebar

Without a sidebar With a single grey sidebar With a double grey sidebar With a single black sidebar With a double black sidebar

Safety vi

A few practical exercises have been included. These could be carried out at home using simple materials that youÂ are likely to have available to you. (There are many more practical activities on the CD-ROM that accompanies your coursebook.) While carrying out such experiments, it is your responsibility to think about your own safety, and the safety of others. If you work sensibly and assess any risks before starting, you should come to no harm. If you are in doubt, discuss what you are going to do with your teacher before you start.

Original material ÂŠ Cambridge University Press 2017

Chapter P1 Making measurements KEY TERMS

density: the ratio of mass to volume for a substance

USEFUL EQUATIONS

density =

mass volume

Exercise P1.01 The SI system of units To be part of the international community of scientists, you need to use the SI units (Le Système International d’Unités). a Give the SI units (name and symbol) of the following quantities: length 1

volume

b Give the name in words and the symbol for the following: one thousand metres

one-thousandth of a metre

c How many centimetres are there in a metre? litres are there in a cubic metre? d List as many non-SI units of length as you can.

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Cambridge IGCSE Combined and Co-ordinated Sciences

e Give a reason why it is important for scientists to have a system of units that is agreed between all countries.

f Name some more professions that make use of the SI system of units.

Exercise P1.02 Accurate measurements To measure a length accurately, it is essential to have a careful technique. This exercise will test your ability to measure lengths. a The diagram shows how a student attempted to measure the length of a piece of wire.

From the diagram, estimate the length of the wire.

State three ways in which the student could have improved his technique for measuring the wire.

b Find a rectangular sheet of paper, at least as big as the pages of this book. A sheet of newspaper is ideal.

Your task is to use a ruler to measure three lengths: the short side, the long side and the diagonal.

For lengths that are longer than your ruler, you will need to devise a careful technique.

c Describe the method you have used for measuring the length of the diagonal. It may help to include a diagram.

Original material © Cambridge University Press 2017

Chapter P1: Making measurements

d Record your results (in centimetres) in Table 1.01.

Measurement

Length / cm

Length2 / cm2

short side long side diagonal Table 1.01 e Now you can use Pythagoras’ theorem to test your results. In the third column of the table, calculate and write down the square of each length.

Then calculate:

(short side)2 + (long side)2 =

This should be equal to (diagonal)2.

f Round off your values to the nearest cm2. How close are your two answers? Write a comment below.

Exercise P1.03 Density data

This exercise presents some data for you to interpret and use. Some data about the density of various solids and liquids are shown in Table 1.02.

Material water ethanol olive oil mercury ice diamond cork chalk iron tungsten aluminium gold

State / type liquid / non-metal liquid / non-metal liquid / non-metal liquid / metal solid / non-metal solid / non-metal solid / non-metal solid / non-metal solid / metal solid / metal solid / metal solid / metal

Density / kg/m3 1000 800 920 13 500 920 3500 250 2700 7900 19 300 2700 19 300

Density / g/cm3 1.000 0.800

Table 1.02 Two units are used for the densities, kg/m3 and g/cm3. a Complete the fourth column by converting each density in kg/m3 to the equivalent value in g/cm3. The first two have been done for you.

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

b Ice floats on water because its density is less than that of water. Name another solid material shown in the table which will float in water.

c A cook mixes equal volumes of water and olive oil in a jar. The two liquids separate. Complete the drawing of the jar to show how the liquids will appear. Label them.

d A student wrote: “These data show that metals are denser than non-metals.” Do you agree? Explain your answer.

e Calculate the mass of a block of gold that measures 20 cm × 15 cm × 10 cm. Give your answer in kg.

Original material © Cambridge University Press 2017

Chapter P1: Making measurements

f A metalworker finds a block of silvery metal. He weighs it and he measures its volume. Here are his results:

mass of block = 0.270 kg

volume of block = 14.0 cm3

Calculate the density of the block.

Suggest what metal this might be.

Exercise P1.04 Testing your body clock How good would your pulse be as a means of measuring time intervals? Galileo used the regular pulse of his heart as a means of measuring intervals of time until he noticed that a swinging pendulum was more reliable. In this exercise, you need to be able to measure the pulse in your wrist. Place two fingers of one hand gently on the inside of the opposite wrist. Press gently at different points until you find the pulse. (Alternatively, press two fingers gently under your jawbone on either side of your neck.) You will also need a clock or watch that will allow you to measure intervals of time in seconds. a Start by timing 10 pulses. (Remember to start counting from zero: 0, 1, 2, 3, …, 9, 10.) Repeat this several times and record your results in a table in the space provided.

b Comment on your results. How much do they vary? Is the problem that it is difficult to time them, or is your heart rate varying?

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

c Use your results to calculate the average time for one pulse.

d Repeat the above, but now count 50 pulses. Record your results in a table in the space provided. Calculate the average time for one pulse.

e Now investigate how your pulse changes if you take some gentle exercise – for example, by walking briskly, or by walking up and down stairs.

Write up your investigation in the lined space. Use the following as a guide. • Briefly describe your gentle exercise. • Give the measurements of pulse rate that you have made. • Comment on whether you agree with Galileo that a pendulum is a better time-measuring instrument than your pulse.

Original material © Cambridge University Press 2017

Chapter P2 Describing motion KEY TERMS

speed: the distance travelled by an object in unit time acceleration: the rate of change of an object’s velocity

USEFUL EQUATIONS

speed =

distance

acceleration =

time

speed = gradient of distance–time graph

change in speed time taken

acceleration = gradient of speed–time graph

distance = area under speed–time graph

Exercise P2.01 Measuring speed This exercise is about how we can measure the speed of a moving object. a One way to find the speed of an object is to measure the time it takes to travel a measured distance. Table 2.01 shows the three quantities involved.

Complete the table as follows: • In the second column, give the SI unit for each quantity (name and symbol). • In the third column, give some other, non-SI, units for these quantities. • In the fourth column, name suitable measuring instruments for distance and time.

Quantity

SI unit (name and symbol)

Non-SI units

Measuring instrument

distance time speed Table 2.01 b In the laboratory, the speed of a moving trolley can be found using two light gates. A timer measures the time taken for a trolley to travel from one light gate to the other. What other quantity must be measured to determine the trolley’s speed?

Write down the equation used to calculate the speed of the trolley

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Cambridge IGCSE Combined and Co-ordinated Sciences

A trolley takes 0.80 s to travel between two light gates, which are separated by 2.24 m. Calculate its average speed.

c The speed of moving vehicles is sometimes measured using detectors buried in the road. The two detectors are about 1 m apart. As a vehicle passes over the first detector, an electronic timer starts. As it passes over the second detector, the timer stops.

Explain how the vehicle’s speed can then be calculated.

On one stretch of road, any vehicle travelling faster than 25 m/s is breaking the speed limit. The detectors are placed 1.2 m apart. Calculate the speed of a car that takes 0.050 s to travel this distance. Is it breaking the speed limit?

Calculate the shortest time that a car can take to cross the detectors if it is not to break the speed limit.

Original material © Cambridge University Press 2017

Chapter P2: Describing motion

d Describe briefly how such a speed-detection system could be used to light up a warning light whenever a speeding car goes past.

Exercise P2.02 Speed calculations Use the equation for speed to solve some numerical problems. a The table shows the time taken for each of three cars to travel 100 m. Circle the name of the fastest car. Complete Table 2.02 by calculating the speed of each car. Give your answers in m/s and to one decimal place.

Car

Time taken / s

red car

4.2

green car

3.8

yellow car

4.7

Speed / m/s

Table 2.02 b A jet aircraft travels 1200 km in 1 h 20 min.

How many metres does it travel?

For how many minutes does it travel?

And for how many seconds?

Calculate its average speed during its flight.

c A stone falls 20 m in 2.0 s. Calculate its average speed as it falls.

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Cambridge IGCSE Combined and Co-ordinated Sciences

The stone falls a further 25 m in the next 1.0 s of its fall. Calculate the stone’s average speed during the 3 s of its fall.

Explain why we can only calculate the stone’s average speed during its fall.

Exercise P2.03 More speed calculations In these problems, you will have to rearrange the equation for speed. 10

a A car is moving at 22 m/s. How far will it travel in 35 s?

b A swallow can fly at 25 m/s. How long will it take to fly 1.0 km?

c A high-speed train is 180 m long and is travelling at 50 m/s. How long will it take to pass a person standing at a level crossing?

Original material © Cambridge University Press 2017

Chapter P2: Describing motion

How long will it take to pass completely through a station whose platforms are 220 m in length?

d In a 100 m race, the winner crosses the finishing line in 10.00 s. The runner-up takes 10.20 s. Estimate the distance between the winner and the runner-up as the winner crosses the line. Show your method of working.

Explain why your answer can only be an estimate.

Exercise P2.04 Distance–time graphs In this exercise, you draw and interpret some distance–time graphs. You can calculate the speed of an object from the gradient (slope) of the graph. a The diagrams A–D show distance–time graphs for four moving objects. Complete Table 2.03 by indicating (in the second column) the graph or graphs that represent the motion described in the first column.

Time

Description of motion

Time

Distance

Time

Graph(s)

moving at a steady speed stationary (not moving) moving fastest changing speed Table 2.03 Original material © Cambridge University Press 2017

Time

Cambridge IGCSE Combined and Co-ordinated Sciences

b Table 2.04 shows the distance travelled by a runner during a 100 m race. Use the data to draw a distance–time graph on the graph paper grid provided.

Distance / m

Time / s

0.0

10.0

25.0

45.0

65.0

85.0

105.0

2.0

4.0

6.0

8.0

10.0

12.0

Table 2.04

Now use your graph to answer these questions:

How far did the runner travel in the first 9.0 s?

How long did the runner take to run the first 50.0 m?

How long did the runner take to complete the 100 m?

Use the gradient of your graph to determine the runner’s average speed between 4.0 s and 10.0 s. On your graph, show the triangle that you use.

c On the graph paper grid provided, sketch a distance–time graph for the car whose journey is described here: • The car set off at a slow, steady speed for 20 s. • Then it moved for 40 s at a faster speed.

Original material © Cambridge University Press 2017

Chapter P2: Describing motion

• Then it stopped at traffic lights for 20 s before setting off again at a slow, steady speed.

d The graph represents the motion of a bus for part of a journey.

1000

Distance / m

800

13 600

400

200

100

Time / s

On the graph, mark the section of the journey where the bus was moving faster.

From the graph, calculate the following: • the speed of the bus when it was moving faster

•

the average speed of the bus.

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

Exercise P2.05 Acceleration When an object changes speed, we say that it accelerates. Its acceleration is the rate at which its speed increases. a In an advertisement, a car is described like this:

“It can accelerate from 0 km/h to 80 km/h in 10 s.”

By how much does its speed increase in each second (on average)?

b A cyclist is travelling at 4.0 m/s. She speeds up to 16 m/s in a time of 5.6 s. Calculate her acceleration.

c A stone falls with an acceleration of 10.0 m/s2. Calculate its speed after falling for 3.5 s.

d On the Moon, gravity is weaker than on Earth. A stone falls with an acceleration of 1.6 m/s2. How long will it take to reach a speed of 10 m/s?

Original material © Cambridge University Press 2017

Chapter P2: Describing motion

Exercise P2.06 Speed–time graphs In this exercise, you draw and interpret some speed–time graphs. You can calculate the acceleration of an object from the gradient (slope) of the graph. You can calculate the distance travelled from the area under the graph. a The diagrams A–D show speed–time graphs for four moving objects. Complete Table 2.05 by indicating (in the second column) the graph or graphs that represent the motion described in the first column.

Time

Speed

Time

Description of motion

Speed

Time

Graph(s)

moving at a steady speed speeding up, then slowing down moving with constant acceleration accelerating to a steady speed Table 2.05

b The graph represents the motion of a car that accelerates from rest and then travels at a steady speed.

Speed / m/s

Time / s

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

From the graph, determine the acceleration of the car in the first part of its journey.

On the graph, shade in the area that represents the distance travelled by the car while accelerating. Label this area A.

Shade the area that represents the distance travelled by the car at a steady speed. Label this area B.

Calculate each of these distances and the total distance travelled by the car. 1 [Note: area of a triangle = × base × height.] 2

c On the graph paper grid, sketch a speed–time graph for the car whose journey is described here: 16

• The car set off at a slow, steady speed for 20 s. • Then, during a time of 10 s, it accelerated to a faster speed. • It travelled at this steady speed for 20 s. • Then it rapidly decelerated and came to a halt after 10 s.

Original material © Cambridge University Press 2017

Chapter P3 Forces and motion KEY TERMS

force: the action of one body on a second body that causes its velocity to change resultant force: the single force that has the same effect on a body as two or more forces mass: the property of an object that causes it to resist changes in its motion weight: the downward force of gravity that acts on an object because of its mass

USEFUL EQUATIONS

Force = mass × acceleration F = ma

Exercise P3.01 Identifying forces Forces are invisible (although we can often see their effects). Being able to identify forces is an important skill for physicists. The pictures show some bodies. Your task is to add at least one force arrow to each body, showing a force acting on it. (Two force arrows are already shown.) 17

Each force arrow should be labelled to indicate the following: • the type of force (contact, drag/air resistance, weight/gravitational, push/pull, friction, magnetic) • the body causing the force • the body acted on by the force. For example: the gravitational force of the Earth on the apple.

Original material © Cambridge University Press 2017

Cambridge IGCSE Combined and Co-ordinated Sciences

Exercise P3.02 The effects of forces A force can change how a body moves, or it may change its shape. a Each diagram shows a body with a single force acting on it. For each, say what effect the force will have.

b A boy slides down a sloping ramp. In the space below, draw a diagram of the boy on the ramp and add a labelled arrow to show the force of friction that acts on him.

What effect will the force have on the boy’s movement?

Original material © Cambridge University Press 2017

Chapter P3: Forces and motion

Exercise P3.03â&#x20AC;&#x201A; Combining forces When two or more forces act on a body, we can replace them by a single resultant force that has the same effect. a In Table 3.01, the left-hand column shows four objects acted on by different forces. For the same objects in the right-hand column, add a force arrow to show the resultant force acting on it in each case. 80 N N 80 80 N 8080 NN

45 N N 45 45 N 4545 NN

60 N N 60 8060 NN 50 N 6050 NN 60 50 N 5050 NN 60 N

40 N N 40 4540 NN 4040 NN

Forces on object

Resultant force

20 N N 20 40 N 20 N 2020 NN 20 N 4520 NN 20 N 20 N 20 N 20 N

50 N 20 N 8020 NN 20 N 2020 NN

40 N N 40 40 N 40 N20 N 20 N N 50 N 20 N 4040 40NN N 20 N 40 20 N 40 N 2020 N N 4040 N 20 N N 80 N NN 100 N 100 N 40 N 45 100 N 100 100 N 100 N 100 NN 100 N 100 20100 N 20 NN N 40 N 20 60 N

60 N

100 N N 40 N 100 100100 N N 100 N 40100 N N

100 N

50 N Table 3.01 20 N

2040NN

100draw N b In the space below, a diagram showing a body with four forces acting on it. Their resultant must be 4 N acting vertically downwards. 20 NN 100

20 N 100 N

40 NN 100 20 N 100 N

40 N 100 N

100 N

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Cambridge IGCSE Combined and Co-ordinated Sciences

Exercise P3.04 Mass and weight Mass and weight are two quantities that can easily be confused. How well do you understand the difference between mass and weight? In the second column of Table 3.02, write ‘mass’ or ‘weight’ (or ‘both’), as appropriate.

Description

Mass or weight or both?

a force measured in kilograms measured in newtons decreases if you go to the Moon a measure of how difficult it is to accelerate a body caused by the attraction of another body increases if more atoms are added to a body balanced by the contact force of the floor when you are standing used in calculating the acceleration of a body when a force acts on it makes it difficult to change the direction of a body as it moves decreases to zero as a body moves far from the Earth or any other object Table 3.02 20

Exercise P3.05 Force, mass and acceleration Here you practise using the relationship F = ma. a The equation F = ma relates three quantities. Complete Table 3.03 to show the names of these quantities and their SI units.

Quantity

Symbol

SI unit

F m a Table 3.03 b Rearrange the equation F = ma to change its subject: m=

c Calculate the force needed to give a mass of 20 kg an acceleration of 0.72 m/s2.

Original material © Cambridge University Press 2017

Chapter P3: Forces and motion

d A car of mass 450 kg is acted on by a resultant force of 1575 N. Calculate its acceleration.

e One way to find the mass of an object is to apply a force to it and measure its acceleration. An astronaut pushes on a spacecraft with a force of 200 N. The spacecraft accelerates at 0.12 m/s2. What is the mass of the spacecraft?

f In the space below, draw a falling stone with the following forces acting on it: • its weight, 8.0 N • air resistance, 2.4 N.

g Calculate the stone’s acceleration. (Its mass is 0.80 kg.)

Original material © Cambridge University Press 2017

Answers Example answers and all questions were written by the author.

Chapter P1 Making measurements

For example, the table should resemble the following (see Table A1.01):

Measurement

Exercise P1.01 The SI system of units

short side long side diagonal

a metre (m)

cubic metre (m3)

c 100

156 299 454

Comments will vary.

Exercise P1.03 Density data

1000

d For example: inch, foot, yard, mile, furlong, etc. e For example: to make it easier to compare measurements; to make it easier to share data 122

12.5 17.3 21.3

(short side)2 + (long side)2 = 156 + 299 = 455

millimetre (mm)

Length2 / cm2

Table A1.01

b kilometre (km)

Length / cm

a see Table A1.02 b cork c

f For example: medicine (doctors, nurses), engineering, architecture and surveying, etc.

Exercise P1.02 Accurate measurements olive oil

6.7 cm

Align end with zero; place next to ruler; straighten it out.

water

b–e Answers will depend on the piece of paper selected by the student.

Material water ethanol olive oil mercury ice diamond cork chalk iron tungsten aluminium gold

Density / kg/m3 1 000 800 920 13 500 920 3 500 250 2 700 7 900 19 300 2 700 19 300

Table A1.02 122

Density / g/cm3 1.000 0.800 0.920 13.500 0.920 3.500 0.250 2.700 7.900 19.300 2.700 19.300

Answers

Quantity

SI unit (name and symbol)

Non-SI units

Measuring instrument

distance

metre (m)

mile, etc.

tape measure, rule

time

second (s)

hour, etc.

clock, stopwatch

speed

metre per second (m/s)

mile per hour, etc.

Table A2.01

d Disagree. Aluminium (metal) is less dense than diamond (non-metal). But it is true that, for the table, most metals are more dense than most non-metals.

Exercise P2.02 Speed calculations a The green car should be circled as the fastest in Table A2.02

e 57.9 kg

Car

f 19 300 kg/m3

red car green car

4.2

23.8

3.8

26.3

yellow car

4.7

21.3

possibly tungsten

b 1 200 000 m

Answers will vary. tudents should recognise that measuring 50 pulses S is better than measuring 10 (provided that the pulse rate is not changing). Also they should appreciate that pulse rate can change, and that this makes it less reliable than using a pendulum.

Chapter P2 Describing motion Exercise P2.1 Measuring speed a see Table A2.01

2.8 m/s

80 min

4800 s

250 m/s

c 10 m/s

15 m/s

It is speeding up (accelerating).

Exercise P2.03 More speed calculations a 770 m b 40 s

b distance travelled speed =

Speed / m/s

Table A2.02

Exercise P1.04 Testing your body clock

Time taken / s

c 3.60 s

distance

time

8.0 s

d 2.0 m

c Knowing the distance between the detectors,

Their speeds might change during the race.

distance

calculate

24 m/s; within the speed limit

0.048 s

time

d If the time taken by a vehicle is equal to or less than 0.048 s, the warning lights are shown.

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Cambridge IGCSE Combined and Co-ordinated Sciences

Exercise P2.04 Distance–time graphs

Exercise P2.05 Acceleration

a see Table A2.03

a 8 km/h

Description of motion

Graph(s)

moving at a steady speed

B, D

stationary (not moving)

moving fastest

changing speed

b 2.1 m/s2 c 35 m/s d 6.25 s

Exercise P2.06 Speed–time graphs

Table A2.03

a see Table A2.04

Description of motion

100

Distance / m

80 60

speeding up, then slowing down

moving with constant acceleration

accelerating to a steady speed

b 1.6 m/s2

20 0

moving at a steady speed

Table A2.04

124

75.0 m

6.5 s

11.5 s

10.0 m/s

Speed / m/s

Time / s

20 B

Distance 0

100

Time / s

Graph(s)

1 × 15 × 24 = 180 m 2

B = 25 × 24 = 600 m

total distance = 780 m

d first section marked as faster

17.5 m/s

10.0 m/s

Speed

Time / s

40 Time / s

Answers

Chapter P3 Forces and motion Exercise P3.01 Identifying forces Forces and labels should be as follows: Apple: (up) air resistance of air on apple; (down) gravitational force of Earth on apple

Car: (up) contact force of road on car; (down) gravitational force of Earth on car; (back) air resistance of air on car; (forwards) push of engine on car

Person on slide: (down) gravitational force of Earth on person; (up slope) frictional force of slide on person; (normal to slope) contact force of slide on person

Fish: (down) gravitational force of Earth on fish; (up) upthrust of water on fish; (back) drag of water on fish; (forwards) thrust caused by fish’s movements, acting on fish

Paperclip: (down) gravitational force of Earth on clip; (up) magnetic force of magnet on clip

Box: (down) gravitational force of Earth on box; (up) contact force of floor on box; (to right) push of person on box; (to left ) frictional force of ground on box

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Cambridge IGCSE Combined and Co-ordinated Sciences

Exercise P3.02 The effects of forces

Exercise P3.04 Mass and weight

a A Van will accelerate / speed up

See Table A3.02

B Van will decelerate / slow down

C Tree will bend over to right

D Ball will accelerate downwards (but follow a curved path)

Description

Mass or weight or both?

a force

weight

measured in kilograms

mass

measured in newtons

weight

decreases if you go to the Moon

weight

a measure of how difficult it is to accelerate a body

mass

caused by the attraction of another body weight

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Friction will make him go slower (better: … reduce his acceleration).

Exercise P3.03 Combining forces a see Table A3.01

increases if more atoms are added to a body

both

balanced by the contact force of the floor when you are standing

weight

used in calculating the acceleration of a body when a force acts on it

mass

makes it difficult to change the direction of a body as it moves

mass

decreases to zero as a body moves far from the Earth or any other object

weight

Table A3.02

Forces on object 80 N

Resultant force 45 N

60 N

40 N

35 N

Exercise P3.05 Force, mass and acceleration

30 N

a see Table A3.03

50 N 20 N 20 N

20 N

Quantity

Symbol SI unit

force

newton (N)

mass

kilogram (kg)

acceleration a 20 N 40 N 20 N 100 N

40 N

Table A3.03 b m =

100 N

a = 40 N

metre per second squared (m/s2)

2.4 N

a F m

c 14.4 N

100 N

d 3.5 m/s2

Table A3.01 b Diagrams will vary; but must show a body with four forces acting on it with resultant 4 N acting vertically downwards.

e 1667 kg (1670 kg) f see diagram on right side.

8.0 N