AP Physics 1 Work Energy and Power Practice Test Name

Transcription

1 AP Physics 1 Work Energy and Power Practice Test Name MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. If there is no air resistance, when they hit the ground A) the heavier one will have half the kinetic energy of the lighter one. B) the heavier one will have twice the kinetic energy of the lighter one. C) the heavier one will have one-fourth the kinetic energy of the lighter one. D) the heavier one will have four times the kinetic energy of the lighter one. 2) A 30-N box is pulled upward 6.0 m along the surface of a ramp that rises at 37 above the horizontal. How much work does gravity do on the box during this process? A) -140 J B) -110 J C) J D) -180 J E) 120 J 3) What is the net power needed to change the speed of a 1600-kg sport utility vehicle from 15.0 m/s to 40.0 m/s in 4.00 seconds? A) 140 kw B) 100 kw C) 10.0 kw D) 14.0 kw E) 275 kw 4) You throw a baseball 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) The work is negative on the way up and on the way down because gravity is always downward. B) The work is negative on the way up and positive on the way down. C) The work is positive on the way up and negative on the way down. D) The work is positive on the way up and positive on the way down. 5) A person carries a 25.0-N rock through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 1.50 min. How much work did gravity do on the rock between A and B? A) 625 J B) 20.0 J C) 75 J D) 275 J E) 0 J 6) Jill does twice as much work as Jack does and in half the time. Jill's power output is A) four times Jack's power output. B) one-fourth as much as Jack's power output. C) twice Jack's power output. D) one-half as much as Jack's power output. E) the same as Jack's power output. 7) It requires 0.30 kj of work to fully drive a stake into the ground. If the average resistive force on the stake by the ground is 828 N, how long is the stake? A) 0.31 m B) 0.41 m C) 0.23 m D) 0.36 m 1

2 8) A truck has four times the mass of a car and is moving with twice the speed of the car. If K t and K c refer to the kinetic energies of truck and car respectively, it is correct to say that A) K t = 16K c. B) K t = 4K c. C) K t = 2K c. D) K t = K c. E) K t = 1 2 Kc. 9) How much work is required to stretch an ideal spring of spring constant (force constant) 40 N/m from x = 0.20 m to x = 0.25 m if the unstretched position is at x = 0.00 m? A) J B) 0.80 J C) 0.45 J D) 1.3 J 10) A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process? A) 90 J B) 0 J C) 900 J D) 180 J E) 45 J 11) A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s. What average force of air friction acted on the stone as it fell? A) 0.13 kn B) 7.2 N C) 2.9 N D) 1.2 N E) 4.1 N 12) Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30, while the slope of the hill of otter 2 is 60. If both start from rest, which otter is moving faster when she reaches the bottom of her hill? A) Otter 1 is moving faster. B) Otter 2 is moving faster. C) The heavier otter is moving faster, no matter which hill she used. D) Both otters have the same speed at the bottom. E) The otter that took the shorter time is moving faster. 13) Three cars (car L, car M, and car N) are moving with the same speed and slam on their brakes. The most massive car is car L, and the least massive is car N. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, for which car is the amount of work done by friction in stopping it the greatest? A) The amount of work done by friction is the same for all cars. B) Car L C) Car N D) Car M 14) 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) P B) 1 12 P C) 6P D) 1 6 P E) 12P 15) A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs. Both springs were initially compressed by the same amount. Which of the following statements about these darts are correct? (There could be more than one correct choice.) A) Both darts move free of the spring with the same speed. B) The heavy dart had more initial elastic potential energy than the light dart. C) The lighter dart leaves the spring moving faster than the heavy dart. D) The darts both have the same kinetic energy just as they move free of the spring. E) Both darts had the same initial elastic potential energy. 2

3 16) A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.) A) Just as they leave the ground, the heavier frog is moving faster than the lighter frog. B) The lighter frog goes higher than the heavier frog. C) Just as they leave the ground, the lighter frog is moving faster than the heavier frog. D) Both frogs reach the same maximum height. E) The heavier frog goes higher than the lighter frog. F) They both leave the ground with the same speed. 17) A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct choice.) A) When they reach the ground, the heavier rock has more kinetic energy than the lighter rock. B) The heavier rock reaches the ground before the lighter rock. C) Both rocks have the same speed when they reach the ground. D) Both rocks have the same kinetic energy when they reach the ground. E) Just as they were released, both rocks had the same amount of gravitational potential energy. 18) A heavy dart and a light dart are launched vertically by identical ideal springs. Both springs were initially compressed by the same amount. There is no significant air resistance. Which of the following statements about these darts are correct? (There could be more than one correct choice.) A) At the maximum height, both darts have the same gravitational potential energy. B) The heavy dart goes higher than the light dart. C) Both darts reach the same maximum height. D) Both darts began moving upward with the same initial speed. E) The light dart goes higher than the heavy dart. 19) A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C? A) 0 m/s B) 20 m/s C) 69 m/s D) 34 m/s E) We cannot solve this problem without knowing the mass of the bead. 20) Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed twice as high as Bill. If there is no air resistance, the maximum height of Joe's ball will be A) roughly 1.4 times that of Bill's ball. B) equal to that of Bill's ball. C) eight times that of Bill's ball. D) four times that of Bill's ball. E) two times that of Bill's ball. 3

4 21) When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed? A) 16H B) 8H C) 4H D) 2H E) 2H 22) A child pulls on a wagon with a force of 75 N. If the wagon moves a total of 42 m in 3.1 min, what is the average power delivered by the child? A) 21 W B) 17 W C) 22 W D) 26 W 23) A stone is released from rest at a height h at the left side of a loop-the-loop, as shown in the figure. There is no appreciable friction from the track or from air resistance. If the radius of the loop is R, what is the minimum height h for which the stone will not fall off the track at the top of the loop? A) 2R B) 2.5 R C) 3.0 R D) 2.0 R E) 3.5 R 24) A 1321-kg car climbs a 5.0 slope at a constant speed of 80.0 km/h. Assuming that air resistance may be neglected, at what rate (in kw) must the engine deliver energy to the drive wheels of the car? A) 48 kw B) 287 kw C) 25 kw D) 38 kw 25) When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high? A) 8V B) 2V C) 4V D) 2V E) 16V 26) In the figure, a ball hangs by a very light string. What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0 m above the bottom of the swing? A) 4.9 m/s B) 4.4 m/s C) 3.1 m/s D) 2.2 m/s 27) A 1500-kg car accelerates from rest to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W) A) 90 hp B) 70 hp C) 60 hp D) 80 hp 4

5 28) A person carries a 2.00-N pebble through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 6.75 min. How much work did gravity do on the rock between A and B? A) J B) J C) 30.0 J D) J E) 56.0 J 29) A 4.0 kg object is moving with speed 2.0 m/s. A 1.0 kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping? A) the 4.0 kg object B) the 1.0 kg object C) Both objects travel the same distance. D) It cannot be determined from the information given. 30) A rock falls from a vertical cliff that is 4.0 m tall and experiences no significant air resistance as it falls. At what speed will its gravitational potential energy (relative to the base of the cliff) be equal to its kinetic energy? A) 8.9 m/s B) 6.3 m/s C) 3.1 m/s D) 13 m/s E) 4.4 m/s 31) 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 1.4 times farther. B) It would have skidded one half as far. C) It would have skidded 4 times farther. D) It would have skidded twice as far. 32) A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 to 15 m? A) 50 J B) 150 J C) 25 J D) 100 J E) 125 J 5

6 33) A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45 above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below if there is no significant air resistance? A) Case A B) Case B C) Case C D) Case D E) The speed will be the same in all cases. 34) Two cyclists who weigh the same and have identical bicycles ride up the same mountain, both starting at the same time. Joe rides straight up the mountain, and Bob rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring friction and wind resistance, which one of the following statements is true? A) The amount of work done by Joe is greater than the amount of work done by Bob, and the average power exerted by Joe is greater than that of Bob. B) Bob and Joe exerted the same amount of work, and the average power of each cyclist was also the same. C) The amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob. D) The average power exerted by Bob and Joe was the same, but Joe exerted more work in getting there. 35) A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed with a light rope. The tree house is 4.0 m above the ground. What is the mass of the box? A) 8.0 kg B) 5.3 kg C) 6.7 kg D) 8.9 kg 6

7 Answer Key Testname: WORK ENERGY AND POWER PRACTICE TEST 1) B 2) B 3) E 4) B 5) E 6) A 7) D 8) A 9) C 10) B 11) E 12) D 13) B 14) E 15) C, D, E 16) C, D 17) A, C 18) A, E 19) D 20) D 21) C 22) B 23) B 24) C 25) B 26) B 27) A 28) D 29) C 30) B 31) C 32) E 33) E 34) C 35) D 7