Exam. Name. TRUE/FALSE. Write ʹTʹ if the statement is true and ʹFʹ if the statement is false. 1) Kinetic energy is proportional to speed.

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1 Exam Name TRUE/FALSE. Write ʹTʹ if the statement is true and ʹFʹ if the statement is false. 1) Kinetic energy is proportional to speed. 2) The gravitational force is a conservative force. 3) If work is done on a system by non-conservative forces, the total mechanical energy of a system stays constant. 4) Work is a vector quantity. 5) Power is a vector quantity. MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 6) You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down. A) Work is - on the way up and - on the B) Work is + on the way up and + on the C) Work is - on the way up and + on the D) Work is + on the way up and - on the 7) How large a force is required to accelerate a 1600 kg car from rest to a speed of 25 m/s in a distance of 200 m? A) 0 N B) 200 N C) 2500 N D) 400 N E) 1600 N 8) Describe the energy of a car driving up a hill. A) gravitational B) elastic C) entirely potential D) entirely kinetic E) both kinetic and potential 9) Two identical balls are thrown from the top of a building with the same speed. Ball 1 is thrown horizontally, while ball 2 is thrown at an angle θ above the horizontal. Neglecting air resistance, which ball will have the greatest speed when hitting the ground below? A) Ball 1 B) Ball 2 C) Cannot be determined without knowing the time each ball is in the air. D) Cannot be determined without knowing the height of the building. E) Both balls reach the ground with the same speed. 10) A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time? A) 12P B) 1 6 P C) P D) 1 12 P E) 6P 11) An object is released from rest a height h above the ground. A second object with four times the mass of the first is released from the same height. The potential energy of the second object compared to the first is A) one-half as much. B) four times as much. C) one-fourth as much. D) eight times as much. E) twice as much. 12) A boy throws a ball to another boy who throws it back with half the original speed. What is the ratio of the final kinetic energy to the initial kinetic energy of the ball? A) 0.50 B) 1.0 C) 0.25 D) 2.00 E)

2 13) A student slides her 80.0-kg desk across the level floor of her dormitory room a distance 4.00 m at constant speed. If the coefficient of kinetic friction between the desk and the floor is 0.400, how much work did she do? A) 3.14 kj B) 24.0 J C) 1.26 kj D) 26.7 J E) 128 J 14) A 20-kg object is resting at the top of a table 1.6 m above ground level. The object is then picked up and moved to a height of 8.7 m above ground level. What is the change in the gravitational potential energy of this object? Use g = 10 m/s2. A) 140 J B) 71 J C) 1740 J D) 1420 J E) 320 J 15) A ball is thrown upward with a speed and direction such that it reaches a maximum height of 16.0 m above the point it was released. At its maximum height it has a speed of 18.0 m/s. With what speed was the ball released? A) 22.2 m/s B) 33.0 m/s C) 36.9 m/s D) 29.2 m/s E) 25.3 m/s 16) A simple pendulum, consisting of a mass m and a string of length L, swings upward, making an angle θ with the vertical. The work done by the tension force is A) mgl cos θ. B) mgl tan θ. C) mgl. D) zero. E) mgl sin θ. 17) An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy? A) 2 B) 4 C) 8 D) 1/4 E) 1/2 18) A 20.0-N weight slides down a rough inclined plane which makes an angle of 30.0 with the horizontal. The weight starts from rest and gains a speed of 15.0 m/s after sliding 150 m. How much work is done against friction? Use g = 10 m/s2. A) 1270 J B) 229 J C) J D) 1500 J E) -229 J 19) You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions? A) It would have skidded one half as far. B) It would have skidded 4 times farther. C) It would have skidded twice as far. D) It would have skidded 1.4 times farther. E) It is impossible to tell from the information given. 20) Consider a plot of the displacement (x) vs. applied force (F) for an ideal elastic spring. The slope of the curve would be A) the reciprocal of the displacement. B) the acceleration of gravity. C) the reciprocal of the acceleration of gravity. D) the reciprocal of the spring constant. E) the spring constant. 2

3 21) An object of mass m with a certain initial speed on a horizontal surface comes to rest after traveling a distance of 10 m. If the coefficient of kinetic friction between the object and the horizontal surface is 0.20, what is the initial speed of the object? Use g = 10 m/s2. A) 8.9 m/s B) 3.6 m/s C) 6.3 m/s D) 7.2 m/s E) 9.8 m/s 22) A kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another kg mass is added to the spring, the potential energy of the spring will be A) the same. B) 4 times as much. C) 3 times as much. D) one-half as much. E) twice as much. FIGURE ) An object of mass = 2 kg is pulled by a constant force F = 4 N for a horizontal distance of 2 m. (Refer to Figure 7-3.) What is the work done along the +x-axis? Neglect friction. A) 9 J B) 5 J C) 2 J D) 8 J E) 7 J FIGURE ) A ball falls from the top of a building, through the air (air friction is present), to the ground below. How does the kinetic energy (K) just before striking the ground compare to the potential energy (U) at the top of the building? A) K is less than U. B) K is equal to U. C) K is greater than U. D) It is impossible to tell. 24) An object of mass 20.0 kg is at rest at the top of an inclined plane whose length is 8.00 m and which makes an angle of 30.0 with the horizontal. The coefficient of kinetic friction between the object and the inclined plane is The object is released and slides down the plane. What is the kinetic energy of this object at the bottom of the inclined plane? Use g = 10.0 m/s2. A) 246 J B) 200 J C) 600 J D) 300 J E) 173 J 26) An object is under the influence of a force as represented by the force vs. position graph as shown in Figure 7-6. What is the work done as it moves from 0 to 10 m? A) 100 J B) 80 J C) 50 J D) 25 J E) 125 J 3

4 FIGURE 8-11 FIGURE 8-7 A 2.0 kg mass is moving along the x-axis. The potential energy curve as a function of position is shown in Figure The system is conservative. There is no friction. 27) Refer to Figure If the speed of the object at the origin is 4.0 m/s, what will be its speed at 4.0 m along the +x-axis? A) 4.6 m/s B) 10 m/s C) 4.0 m/s D) 4.4 m/s E) 4.1 m/s FIGURE 8-6 Two masses M1 = 2.0 kg and M2 = 4.0 kg are attached by a string as shown in Figure 8-7. M1 falls vertically down and M2 moves on a frictionless surface. Initially the system is at rest. Use g = 10 m/s2. 29) Refer to Figure 8-7. What is the potential energy of the mass M1 just before it touches the ground? A) 2.5 J B) 4 J C) 2.3 J D) 5.2 J E) 0 J FIGURE 8-8 A roller coaster of mass 80.0 kg is moving with a speed of 20.0 m/s at position A as shown in Figure 8-6. The vertical height at position A above ground level is 200 m. Neglect friction and use g = 10.0 m/s2. 28) What is the total energy of the roller coaster at point B? A) J B) J C) J D) J E) There is not enough information to solve this problem. 30) An object of mass 2.00 kg starts at rest from the top of a rough inclined plane of height 20.0 m as shown in Figure 8-8. If the work done by the force of friction is -150 J, what is the speed of the object as it reaches the bottom of the inclined plane? Use g = 10.0 m/s2. A) 150 m/s B) 10.0 m/s C) 20.0 m/s D) 15.8 m/s E) 200 m/s 4

5 FIGURE 8-9 An object with a mass of 10.0 kg is at rest at the top of a frictionless inclined plane of height 8.00 m and an angle of inclination 30.0 with the horizontal. The object is released from this position and it stops at a distance d from the bottom of the inclined plane along a horizontal surface, as shown in Figure 8-9. The coefficient of kinetic friction for the horizontal surface is and g = 10.0 m/ s2. 31) Refer to Figure 8-9. At what horizontal distance from the bottom of the inclined plane will this object stop? A) 15.0 m B) 20.0 m C) 25.0 m D) 10.0 m E) 5.00 m SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. 32) Lisa runs up 4 flights of stairs in 22. seconds. She weighs 510. Newtons. If each flight rises 310. cm: (a) What is her change in potential? (b) What average power (watts) was required during the 22. s? (c) What minimum horsepower motor would be required to do this? 5

6 Answer Key Testname: AP 7+8 SAMPLES 1) FALSE 2) TRUE 3) FALSE 4) FALSE 5) FALSE 6) C 7) C 8) E 9) E 10) A 11) B 12) C 13) C 14) D 15) E 16) D 17) D 18) A 19) B 20) D 21) C 22) B 23) A 24) A Diff: 3 25) E 26) A 27) D 28) A 29) E 30) D 31) B Diff: 3 32) (a) 6.32 kj (b) 287. watts (c) hp Diff: 3 6