Physics 201, Midterm Exam 2, Fall Answer Key

Transcription

1 Physics 201, Midterm Exam 2, Fall 2006 Answer Key 1) A constant force is applied to a body that is already moving. The force is directed at an angle of 60 degrees to the direction of the body s velocity. What is most likely to happen is that A. the body will stop moving. B. the body will move in the direction of the force. C. the body s velocity will increase in magnitude but not change direction. D. the body will gradually change direction more and more toward that of the force while speeding up. E. the body will slow down to a stop and then move in the direction of the force. 2) A machine can accelerate pucks on frictionless ice. Starting from rest, the puck travels a distance x in time t when a constant force F is applied. If a constant force 3F is applied, the distance the puck travels in time t is A. x/3 B. 3x/2 C. 3x D. 9x/2 E. 9x

2 3) The total force, applied at an angle θ, needed to drag a box at constant speed across a horizontal surface with coefficient of kinetic friction µ k is A. mg! µ k mgcos" B. mg! µ k mgsin" mg C. cos! " µ k sin! µ D. k mg cos! + µ k sin! E. None of the above 4) A heavy weight is supported by two cables that exert tensions of magnitude T 1 and T 2. Which statement is correct? A. T 1 = T 2 B. T 1y = T 2y C. T 1 > T 2 D. T 1 < T 2 E. We need the mass of the box in order to determine the correct answer.

3 5) The horizontal surface, on which the objects shown in the figure slide, is frictionless. If M = 2.0 kg, the tension in string-1 is 12 N. Determine F. A. 25 N B. 20 N C. 30 N D. 35 N E. 40 N 6) In order to jump off the floor, the floor must exert a force on you A. in the direction of and equal to your weight. B. opposite to and equal to your weight. C. in the direction of and less than your weight. D. opposite to and less than your weight. E. opposite to and greater than your weight.

4 7) A roller-coaster car has a mass of 500 kg when fully loaded with passengers. The car passes over a hill of radius 15 m, as shown. At the top of the hill, the car has a speed of 8.0 m/s. What is the force of the track on the car at the top of the hill? A. 7.0 kn up B. 7.0 kn down C. 2.8 kn down D. 2.8 kn up E. 5.6 kn down 8) A rock attached to a string swings in a vertical circle. Which free body diagram could correctly describe the force(s) on the rock when the string is in one possible horizontal position?

5 9) A 2.0-kg projectile moves from its initial position to a point that is displaced 20 m horizontally and 15 m above its initial position. How much work is done by the gravitational force on the projectile? A kj B kj C. +30 J D. 30 J E. 50 J 10) The horizontal surface on which the block slides is frictionless. The speed of the block before it touches the spring is 6.0 m/s. How fast is the block moving at the instant the spring has been compressed 15 cm? k = 2.0 kn/m, m = 2.0 kg A. 3.7 m/s B. 4.4 m/s C. 4.9 m/s D. 5.4 m/s E. 14 m/s

6 11) Carts A and B have equal masses and travel equal distances D on side-by-side straight frictionless tracks while a constant force F acts on A and a constant force 2F acts on B. Both carts start from rest. The velocities v A and v B of the bodies at the end of distance D are related by A. v B = v A B. v B = v A C. v B = 2 v A D. v B = 4 v A E. v A = 2v B 12) Two clowns are launched from the same spring-loaded circus cannon with the spring compressed the same distance each time. Clown A has a 40-kg mass; clown B a 60- kg mass. The relation between their speeds at the instant of launch is A. v A = 3 2 v B B. v A = 3 2 v B C. v A = v B D. v B = 3 2 v A E. v B = 3 2 v A

7 13) A 0.04-kg ball is thrown from the top of a 30-m tall building (point A) at an unknown angle above the horizontal. As shown in the figure, the ball attains a maximum height of 10 m above the top of the building before striking the ground at point B. If air resistance is negligible, what is the value of the kinetic energy of the ball at B minus the kinetic energy of the ball at A (K B K A )? A. 12 J B. 12 J C. 20 J D. 20 J E. 32 J 14) Cubical blocks of mass m and side l are piled up in a vertical column. The total gravitational potential energy of a column of three blocks is A. mgl B. 3mgl C. 9mgl/2 D. 6mgl E. 9mgl

8 15) Objects A and B, of mass M and 2M respectively, are each pushed a distance d straight up an inclined plane by a force F parallel to the plane. The coefficient of kinetic friction between each mass and the plane has the same value µ k. At the highest point, A. K A = Fd = K B B. K A = (F! µ k Mg cos")d ; K B = (F! 2µ k Mgcos")d C. K A = (F! Mgsin")d ; K B = (F! 2Mgsin")d D. K A = (F + Mgsin! " µ k Mgcos!)d ; K B = (F + Mgsin! " 2µ k Mgcos!)d E. K A = (F! Mgsin"! µ k Mgcos")d ; K B = (F! 2Mgsin"! 2µ k Mgcos")d 16) Identical masses m are attached to identical springs of spring constant k suspended from the ceiling. With both masses hanging in their equilibrium positions, mass A is pulled down 10 cm and released, while mass B is pushed up 10 cm and released. Which statement is correct? A. Mass A will travel a smaller distance to its highest point than mass B will travel to its lowest point. B. Mass A will travel a greater distance to its highest point than mass B will travel to its lowest point. C. Masses A and B will travel equal distances between their highest and lowest points. D. More work was done on mass A by the extending force than on mass B by the compressing force. E. The total work done on mass A by the extending force was equal to the total work done on mass B by the compressing force.

9 17) A 10-g bullet moving 1000 m/s strikes and passes through a 2.0-kg block initially at rest, as shown. The bullet emerges from the block with a speed of 400 m/s. To what maximum height will the block rise above its initial position? A. 78 cm B. 66 cm C. 56 cm D. 46 cm E. 37 cm 18) A ball falls to the ground from height h and bounces to height h. Momentum is conserved in the ball-earth system A. no matter what height h it reaches. B. only if h < h. C. only if h = h. D. only if h > h. E. only if h h.

10 19) Kindergartners, Amanda (Mass 30 kg), Bob (Mass 35 kg), Charlie (Mass 40 kg) and Diane (Mass 45 kg) slide down frictionless slide and are launched at an angle, θ, is fixed by the shape of the slide. Who reaches the maximum height y? A. Amanda B. Bob C. Charlie D. Diane E. All four reach the same height y 20) A block of mass m rests on a horizontal, frictionless surface as shown in the figure. The block is pressed against a light spring having a spring constant k. If the block is released when the spring is compressed a distance x, what is the maximum length d the block reaches along the frictionless incline plane of angle θ? kx 2 A. d = 2mgsin! kx 3 B. d = mgh sin! kxh C. d = 2mgsin! k 2 x 3 D. d = m 2 g 2 cos! E. None of the above