Topic 3 lesson 5 example paper 2 question p v graphs

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SECTION B This section consists of four questions: B1, B2, B3 and B4. Answer any two questions in this section.

B1. This question consists of two parts. Part 1 is about thermodynamics and Part 2 is about a collision between hanging masses.

Part 1 Thermodynamics of two-stage gas process This question is about pressure, volume and temperature changes of an ideal gas.

An ideal gas is enclosed in a cylinder fitted with a moveable piston. The gas undergoes two processes, as follows: First process: The gas, initially in state 1, is expanded at constant temperature T1 until its volume is doubled.

This is state 2. The two states are represented in the diagram below.

Change at constant temperature

State 1 Pressure: P1 Volume: V1 Temperature: T1 (a)

State 2 Pressure: P2 = ?

Volume: V2 = 2V1 Temperature: T2 = T1

Using the axes below, sketch a graph to show how pressure and volume are related for this process. The data point for state 1 is shown plotted. Label the state reached as state 2.

[2]

Pressure

P1

0 0

V1

Volume (This question continues on the following page)

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(Question B1 part 1 continued) (b)

Explain in terms of motions of the gas molecules, why the pressure decreases when the volume increases.

[2]

......................................................................... ......................................................................... ......................................................................... ......................................................................... (c)

Explain whether or not in this process (i)

[2]

work is done by or on the gas. ..................................................................... ..................................................................... .....................................................................

(ii)

the internal energy of the gas changes.

[1]

..................................................................... .....................................................................

[2]

(iii) thermal energy flows into or out from the gas. ..................................................................... ..................................................................... (d)

Explain how the work done, if any, is related to the thermal energy transfer.

[2]

......................................................................... ......................................................................... .........................................................................

(This question continues on the following page)

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(Question B1 part 1 continued) Second process: The piston is now kept fixed, and the gas is heated until the pressure returns to its original value P1 .

This is state 3 and is represented in the diagram below.

Change at constant volume

State 2 Pressure: P2 = ?

Volume: V2 = 2V1 Temperature: T2 = T1 (e)

State 3 Pressure: P3 = P1 Volume: V3 = 2V1 Temperature: T3 = ?

Using the axes below sketch a graph to show how pressure varies with absolute temperature for this process. The data point for state 2 is shown plotted. Label the state reached as state 3.

[2]

Pressure

P2

0 0 (f)

T1

Absolute temperature

Explain in terms of the motions of the gas molecules, why the pressure increases when the gas is heated.

[3]

......................................................................... ......................................................................... ......................................................................... .........................................................................

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(Question B1 part 1 continued) (g)

Explain whether or not for this process (i)

work is done.

[2]

..................................................................... ..................................................................... (ii)

the internal energy of the gas changes.

[1]

..................................................................... ..................................................................... (h)

If the initial temperature of the gas in state 1 is 20 DC , determine the final temperature of the gas in state 3, after both processes.

[3]

......................................................................... ......................................................................... ......................................................................... .........................................................................

(This question continues on the following page)

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