University of the Philippines College of Science
Physics 71 Set A First Long Exam First Semester AY 2010-2011
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Physics 71/First Long Exam A
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1st Sem AY 2010-2011
Instructions: Choose the letter of the best answer. Ignore air resistance unless stated other m wise. The acceleration due to gravity is: g = 9.81 s2 . 1. Displacement Consider the following position versus time plot of a remote controlled toy car moving in one dimension. For the entire 10.0 seconds, what is the average velocity of the car? (a)Zero (b)0.5 ms (c)0.8 ms (d)1.0 ms (e)2.0 ms
2. Can’t you see. A particle moves in a straight line with displacement ∆x for a time interval ∆t. Its average velocity at the time interval is vx,av , and its velocity is vx (t) at time t within the interval. Which of the following conditions implies that vx (t) = vx,av for all t? ∆x (a)∆x > ∆t (d)vx,av = ∆t (b)∆x = ∆t (e)vx is constant in time (c)∆x < ∆t 3. Average Velocity. A motorist makes a trip of 100.0 [km] along a straight km line in one direction. For the first 40.0 [km], he drives at a constant speed of 25.0 hr . At what constant speed must he kmdrive for the remaining distance if his average velocity for the total trip is to be 50.0 hr ? km km km km (a)150. km (b)75.0 (c)66.7 (d)37.5 (e)25.0 hr hr hr hr hr 4. Motion plot. A particle moving in one dimension has the following position vs time plot. At point C, what can you say about the particle’s velocity vx and acceleration ax ? (a)vx < 0 and ax > 0 (b)vx > 0 and ax > 0 (c)vx = 0 and ax = 0 (d)vx = 0 and ax < 0 (e)vx = 0 and ax > 0
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
5. Bumabagal. Which of the following statements is NECESSARILY TRUE about the acceleration ax of a runner slowing down a straight track? (a)ax = 0
(d)The direction of ~a is opposite to the direction of motion.
(b)ax < 0
(e)The direction of ~a is oriented along the direction of motion.
(c)ax > 0
6. Bugatti. Mayraluna bought a new Bugatti Veyron sports car. Her car can reach a speed m of 111 s from rest in 50.0 [s] on a straight track. What is the magnitude of the car’s maximum average acceleration? (b)2.22 sm2 (c)4.45 sm2 (d)27.8 sm2 (e)55.5 sm2 (a)0.450 sm2 7. Constant Acceleration. The position of ma train that2 moves m along a downhill track is described by the function x(t) = 15.00 s t + 8.00t s2 . What is the acceleration of the train? (a)16.0 sm2 (b)15.0 sm2 (c)8.00 sm2 (d)4.00 sm2 (e)0 sm2 8. Tag. A cop, initially at rest, spotted a thief at a distance d and is running running directly away from him at a constant speed v. He immediately ran towards the thief and caught the latter after a time t. What must be the cop’s acceleration, assuming that it is constant? v (d + vt) (d + vt) 2(d + vt) 2d (b) (c) (d) (e) (a) 2 t t 2t2 t2 t2 9. Freely m Falling Bodies I. A ball is thrown vertically upwards with an initial speed of 3 s . What is the velocity of the ball at the maximum height of its trajectory? (a)−3 ms (b)0 ms (c)3 ms 10. Freely Falling Bodies II Three balls are thrown from a height of 10 m from the ground. Ball A is released from rest. Ball m B is thrown vertically upward with a speed of 3 s . Ball C is thrown vertically m downwards with a speed of 3 s . Which of the balls will reach the ground with the greatest speed? (a)Ball A (b)Ball B (c)Ball C
(d)Balls B and C (e)Balls A, B and C
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
11. Dropped stone. A stone is dropped from rest at the roof of a building. How far below the roof is the stone after 1.50 [s]? (a)5.52 [m] (b)7.36 [m] (c)11.0 [m] (d)14.7 [m] (e)22.1 [m]
12. Vectors. Position vectors for a particle are plotted at time tinitial = 0 [s] and tf inal = 3 [s] as shown in the figure at the right. What is the y-component of the average velocity of the particle from time tinitial to tf inal ? −2y0 (a)0 (d) 3 [s] (b)2y0 3y0 2y0 (e) (c) 2 [s] 3 [s]
13. Robot motion A remote-controlled robot is moving along the x − y plane. The plots of the horizontal (x) and vertical (y) positions as functions of time t are shown in the figure. What is the speed of the robot at t = 5.0 [s]? (a)3.5 ms (d)5.8 ms (b)4.0 ms (e)29. ms (c)5.0 ms 14. Projectile Motion I. Two identical objects A and B were released simultaneously from the same height. Object A was dropped while object B shot off with a horizontal speed v0 . Which of object will have the greatest time of flight? (a)Object A (b)Object B (c)Both objects have the same time of flight.
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
15. Projectile Motion II. A happy Physics 71 student kicked a ball hard, making it fall off an edge of a cliff. Right m at the edge, the ball’s velocity is 5.00 s in the horizontal direction as shown in the figure. How far is the ball away from the cliff (d) after it has fallen for 0.800 [s]? (a)6.25 [m] (b)5.08 [m] (c)4.00 [m]
(d)3.14 [m] (e)2.48 [m]
16. Champion! For the penalty kick, Lionel Messi was assigned to kick the football which was on the ground, a horizontal distance of 11.0 [m] away from the goal. Messi hit the m ◦ ball at a speed of 11.0 s , 45.0 above the horizontal. What was the height of the ball when it is at the goal? (a)0.000 [m] (b)0.396 [m] (c)1.19 [m] (d)7.77 [m] (e)11.0 [m] 17. Uniform circular motion. Which of the following statements is true about a particle moving in uniform circular motion? (a)Its acceleration is directed radially outward from the center of the circular path. (b)Its acceleration has a nonzero component parallel to its velocity. (c)Its velocity is always parallel to its acceleration. (d)Its velocity always changes in direction. 18. Bug Master. A bug stuck in a blade of an electric fan is moving in uniform circular motion along a radius R and speed v. Which of the following correctly describes the bug’s acceleration? (a)It is tangent to the circular path at any point. (b)Its magnitude is 9.8 sm2 and is directed to the ground. (c)Its magnitude is greatest when the bug is at the topmost point of its path. (d)Its magnitude is constant and its direction is towards the center of the circular path.
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
19. Bus Stop A passenger sits on a bus that is moving at constant speed from bus stop A towards bus stop B. Which of the following statements is true? (a)For a person standing on bus stop A, the passenger is moving towards him. (b)For a person standing on bus stop A, the passenger is moving away from him. (c)For a person standing on bus stop B, the passenger is moving away from him. (d)For the passenger on the bus, the person at bus stop A is not moving. (e)For the passenger on the bus, the person at bus stop B is not moving. 20. Relative m Velocity I. Agent 007 is on a long cargo truck that mis running forward at 10 s on a highway. A police car is chasing the truck at 15 s from behind. How should Agent 007 run such that he is at rest relative to the police car? (a)The agent should stay still on top of the truck. (b)The agent should run with a speed of 5 ms towards the front of the cargo truck. (c)The agent should run with a speed of 10 ms towards the front of the cargo truck. (d)The agent should run with a speed of 5 ms towards the back of the cargo truck. (e)The agent should run with a speed of 10 ms towards the back of the cargo truck. 21. Relative Velocity II. After an intersection, two cars are moving away from each other at different directions. The first car is moving at 56.0 [kph] ˆj, while the second car heads at -33.0 [kph] ˆi. What is the velocity of the first car as observed by a stationary passenger of the second? (a)+33 [kph] ˆi + 56 [kph] ˆj (c)−33 [kph] ˆi + 56 [kph] ˆj (b)+33 [kph] ˆi − 56 [kph] ˆj
(d)−33 [kph] ˆi − 56 [kph] ˆj
22. Frame Up! Which of the following object/s can be used as an inertial reference frame? (a)A freely falling rock (b)A runner who is speeding up (c)A stationary inclined plane (d)A slingshot under uniform circular motion (e)Both A and B
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
23. Step Up! A cart (of weight W ) is lifted up at constant speed by a steel cable attached to an electric pulley. Assuming there are no resistive forces, and that the mass of the steel cable is negligible compared to the mass of the cart, what can we conclude about the of force T~ , exerted by the cable on the cart? (a)T < W , T~ is directed downward (b)T > W , T~ is directed downward (c)T < W , T~ is directed upward (d)T > W , T~ is directed upward (e)T = W , T~ is directed upward For the next two questions, consider a 2 [kg] box on a frictionless plane that is inclined at an angle of 30◦ with the horizontal. A force F~ is applied on the box with the direction parallel to the incline as shown in the figure. 24. Box on incline I. What is the magnitude of the normal force exerted by the plane on the box? (a)17.0 [N] (b)9.81 [N] (c)19.6 [N]
(d)11.3 [N] (e)34.0 [N]
25. Box on incline II. What is the magnitude of the force F~ to prevent the box from sliding down? (a)34.0 [N] (b)19.6 [N] (c)17.0 [N] (d)11.3 [N] (e)9.81 [N] 26. Falling Watermelon What is the force exerted by Earth on a 1.50 kg watermelon in free fall? (a)9.81 N upward (b)14.7 N upward (c)0 N
(d)14.7 N downward (e)9.81 N downward
27. Balikbayan box A 50.0-[kg] balikbayan box slides down a very smooth ramp inclined at an angle 15.0◦ . If it starts from rest at the top of the ramp, how far will it have moved after 1.00 [s]? (a)1.27 [m] (b)2.54 [m] (c)4.74 [m] (d)4.91 [m] (e)9.48 [m]
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
28. Weight Conscious A child weighs 147.[N] on the surface of Earth and weighs 27.2 [N] on the surface of Io, one of Jupiter’s moons. What is the magnitude of the acceleration due to gravity near the surface of Io? (a)53.1 sm2 (b)9.81 sm2 (c)5.41 sm2 (d)1.81 sm2 (e)0.180 sm2
29. The Pair. A book is at rest on top of a flat table. Which of the following is the reaction force to the weight of the book? (a)force due to the table on the book (b)force due to the book on the table (c)force due to Earth on the book (d)force due to the book on Earth 30. Soccer Ball. A soccer ball resting at the ground was kicked with a force F~ projected 30◦ above the ground. The ball then underwent projectile motion. What is the free body diagram of the ball at the peak of its trajectory?
31. Picture Frame. A stationary 0.300[kg] picture frame hangs from a nail by a single string, as shown in the figure. What is the tension in the string? (a)1.47 N (b)1.52 N (c)3.05 N
(d)5.69 N (e)11.4 N
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
32. Two boxes. Box A is on top of Box B, and box B is on a flat table. The boxes and the table are all at rest. Which of the following is TRUE? I. The force exerted by box B on box A is equal in magnitude to the weight of box A. II. The force exerted by the table on box B is equal in magnitude to the weight of box B. III. The force exerted by the table on box B is equal in magnitude to the force exerted by box A on box B. (a)I only (b)II only (c)I and II only
(d)I and III only (e)I,II and III
33. Up-Right. Two forces are simultaneously acting on a 4.0 kg object on top of a frictionless surface. The forces are 12 [N] upward and 16 [N] to the right, yielding a net force as shown in the figure. What is the magnitude of the acceleration of the object and what is the angle θ? (d)20. sm2 ; 37◦ (a)5.0 sm2 ; 37◦ (b)5.0 sm2 ; 53◦ (e)20. sm2 ; 53◦ (c)10. sm2 ; 0◦ 34. Elevator cable The cable supporting a 2125 [kg] elevator can withstand a maximum tension of 21750 [N]. What is the maximum upward acceleration of the elevator can the cable withstand? (a)0.425 sm2 (b)1.65 sm2 (c)9.24 sm2 (d)10.2 sm2 (e)20.0 sm2 35. Against the Rough Ceiling. A 1.00 [N] block is pushed against the ceiling by a 3.50[N] force at a 60◦ angle as shown in the diagram. The coefficient of static friction between the block and the ceiling is 0.900. If the block is in equilibrium, what is the magnitude of the frictional force acting on the block. (a)0.90[N] (b)1.75[N] (c)1.82[N]
(d)2.73[N] (e)3.63[N]
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
36. Tulak. You and your friend push a heavy box at the same time along a rough level. You exerted 4.0 N East and your friend exerted 3.0 N North as shown in the figure. However, the box remains at rest. The frictional force must then be directed at an angle θ South of West. What is θ? (a)37◦ (b)53◦ (c)127◦ (d)217◦ (e)233◦
37. Move it. A 5.0-[kg] box is at rest on a ramp inclined at an angle of 15◦ . The coefficients of static and kinetic friction are µs = 0.60 and µk = 0.20, respectively. If you push the box downward along the ramp, what is the minimum amount of force that you must apply on the box for the box to start moving? (a)3.2 N (b)9.5 N (c)16 N (d)28 N (e)29 N 38. Tangent. A ball attached to an inextensible string is whirled in a circular motion clockwise along the xy-plane. The string is cut at the instant the ball is in the x axis as shown in the figure. In what direction will the ball move after the string was cut? (a)-x direction (b)+x direction (c)still in circular path
(d)-y direction (e)+y direction
39. Normal force A curve of radius 150-m is banked at an angle of 100 . An 800.-kg car passes through the curve at 16.1 ms without skidding. What is the normal force on the tires exerted by the pavement? (a)8.72 × 101 [N] (b)4.94 × 102 [N] (c)1.71 × 103 [N]
(d)7.96 × 103 [N] (e)4.52 × 105 [N]
40. Unbanked. What is the minimum coefficient of friction required to prevent a car with mass M from sliding in an unbanked curve with radius R if the velocity of the car is V? √ 2 2V gR 2V 2 V2 gR (a) (b) (c) (d) 2 (e) 2 gR gR gR V 2V
Physics 71/First Long Exam A
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1st Sem AY 2010-2011
41. Let’s play ball! You throw a baseball straight up in the air. Which of the following statements is TRUE about the motion of the ball? (a)The instantaneous acceleration at the maximum height is greater than the instantaneous acceleration just before the ball hits the ground. (b)The average acceleration for the whole time that the ball is in the air is equal to the instantaneous acceleration at any time that the ball is in air. (c)The average acceleration for the time that the ball is rising is less than the average acceleration for the time that the ball is falling down. (d)The instantaneous acceleration of the ball when it is at the maximum height is zero. 42. Paint Job. Suppose you’re on top of a ladder to paint a high area on a wall. You forgot your paint brush so instead of going back down, you ask your friend to throw you the brush but you fail to catch it. The brush passes your outstretched hand after 0.50 s and it passes again on its way down 1.30 s after your friend throws it up. What is the vertical distance between your outstretched hand and the release point of the brush? (a)1.20 [m] (b)1.60 [m] (c)3.20 [m]
(d)8.30 [m] (e)15.9 [m]
43. Accelerate! A particle is moving along a curved path with increasing speed. Figure A shows its velocity vector, v, at some point on the path. Which of the following vectors in Figure B correspond to the particle’s acceleration at this point?
Figure A
Figure B
Physics 71/First Long Exam A
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44. Trebuchet. You want to throw your trash outside your yard, with the specifications shown in the figure. What minimum speed must you throw your trash to clear the thin wooden wall? (d)50.5 ms (a)6.26 ms (b)7.10 ms (e)70.6 ms (c)8.40 ms 45. 2nd Law’s Plot The graph of velocity versus time of the particle moving in one dimension is shown at the right. Which graph below shows the net force experienced by the particle?
End of First Long Exam
1st Sem AY 2010-2011