Unless otherwise specified, use g = 9.80 m/s2

Transcription

1 Phy 111 Exam 2 March 10, 2015 Name Section University ID Please fill in your computer answer sheet as follows: 1) In the NAME grid, fill in your last name, leave one blank space, then your first name. 2) Write your ID number in the IDENTIFICATION NUMBER section of the sheet. 3) Write your recitation section number in the spaces K,L in the SPECIAL CODES section. Single digits should be preceded by a 0 (e.g. section 1 is written as 01). 4) Fill in the circles on the sheet corresponding to the letters or numbers of your name, ID and section with a #2 pencil. Unless otherwise specified, use g = 9.80 m/s2 MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) If the net work done on an object is negative, then the objectʹs kinetic energy A) increases. B) remains the same. C) is zero. D) decreases. E) cannot be determined without knowing the object mass. 1) Three applied forces, F1 = 20.0 N, F2 = 40.0 N, and F3 = 10.0 N act on an object with a mass of 2.00 kg which can move along an inclined plane as shown in the figure. Questions 2 and 3 refer to the instant when the object has moved m along the surface of the inclined plane in the upward direction. 2) What is the work done by force F2 as the object moves up the inclined plane? A) 12.0 J B) 16.0 J C) 20.8 J D) 24.0 J E) 0 J 2) 3) What is the work done by the force F3 as the object moves up the inclined plane? A) 20.8 J B) 0 J C) 16.0 J D) 12.0 J E) 24.0 J 3) 1

2 A mass is attached to one end of a string. The other end of the string is attached to a rigid support. The mass is released at A and swings in a vertical arc to points B, C, and D, as shown in the Figure. Neglect air resistance. 4) Refer to Figure above. At what point does the mass have the most kinetic energy? A) A B) B C) C D) D E) none of the given points 4) 5) You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road as the car is slowed by friction between the tires and the 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 as far. C) It would have skidded 1.4 times as far. D) It would have skidded twice as far. E) It is impossible to tell from the information given. 5) 6) A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill. Which rises to a greater height? A) The light object, because it has smaller kinetic energy. B) They both slide to the same height. C) The heavy object, because it has greater kinetic energy. D) The lightweight object, because it weighs less. E) The heavy object, because it weighs more. 6) 7) An object of mass 4 kg is thrown vertically upwards from ground level with an initial speed of 20 m/s. Ignore friction. What is the kinetic energy of the object as it reaches its maximum height? A) 800 J B) 0 J C) 400 J D) 80 J E) 200 J 7) 2

3 FIGURE 8-6 A roller coaster of mass 80.0 kg is moving with a speed of 20.0 m/s at position A as shown in the figure above. The vertical height at position A above ground level is 200 m. Neglect friction and use g = 10.0 m/s2. 8) What is the speed of the roller coaster at point B? A) 66.3 m/s B) 17.6 m/s C) 46.9 m/s D) 20.0 m/s E) There is not enough information to solve this problem. 8) 9) A ping-pong ball moving east at a speed of 4 m/s, collides with a stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision? A) the bowling ball B) Neither; both experienced the same magnitude impulse. C) the Ping-Pong ball D) Itʹs impossible to tell since the actual mass values are not given. E) Itʹs impossible to tell since the velocities after the collision are unknown. 9) 10) A kg baseball is dropped from rest from a height of 2.2 m above the ground. It rebounds to a height of 1.6 m. What change in the ballʹs momentum occurs when the ball hits the ground? (hint: you can use conservation of energy to calculate velocities). A) 1.70 kg m/s upwards B) kg m/s upwards C) kg m/s upwards D) kg m/s downwards E) kg m/s downwards 10) 11) A 3.0-kg object moves to the right at 4.0 m/s. It collides head-on with a 6.0-kg object moving to the left at 2.0 m/s. Which statement is correct? A) The total momentum before the collision is 24 kg m/s, and after the collision is 0 kg m/s. B) The total momentum both before and after the collision is zero. C) The total momentum both before and after the collision is 24 kg m/s. D) The total momentum before the collision is 0 kg m/s, and after the collision is 24 kg m/s. E) None of the above is true. 11) 3

4 12) A fan is turned off, and its angular speed decreases from 10.0 rad/s to 6.3 rad/s in 5.0 s. What is the magnitude of the angular acceleration of the fan? A) 0.86 rad/s2 B) 1.16 rad/s2 C) 11.6 rad/s2 D) 0.74 rad/s2 E) 0.37 rad/s2 12) 13) A child is riding a merry-go-round which completes one revolution every 8.36 s. The child is standing 4.65 m from the center of the merry-go-round. What is the magnitude of the centripetal acceleration of the child? A) m/s2 B) 6.84 m/s2 C) m/s2 D) 3.94 m/s2 E) 2.63 m/s2 13) 14) A Ferris wheel of radius 8.00 m rotates at a constant rate, completing one revolution in 30.0 s. What is the apparent weight of a 60.0-kg passenger when she is at the top of the wheel? A) 567 N B) 432 N C) 325 N D) 615 N E) 589 N 14) 15) A boy and a girl are riding on a merry-go-round that is turning. The boy is twice as far as the girl from the merry-go-roundʹs center. If the boy and girl are of equal mass, which statement is true about the boyʹs moment of inertia with respect to the axis of rotation? A) His moment of inertia is 4 times the girlʹs. B) His moment of inertia is twice the girlʹs. C) The moment of inertia is the same for both. D) The boy has a greater moment of inertia, but it is impossible to say exactly how much more. E) The boy has a smaller moment of inertia, but it is impossible to say exactly how much smaller. 15) 16) Two equal forces are applied to a door at the doorknob. The first force is applied perpendicular to the plane of the door; the second force is applied at 30 to the plane of the door. Which force exerts the greater torque about the hinge line? A) the second applied at an angle B) both exert zero torques C) the first applied perpendicular to the door D) both exert equal non-zero torques E) Additional information is needed. 16) 4

5 17) An 82.0 kg-diver stands at the edge of a light 5.00-m diving board, which is supported by two pillars 1.60 m apart, as shown in the figure above. Find the force exerted by pillar B on the board. (assume the board is massless) A) 1.71 kn downwards B) 3.44 kn upwards C) 2.51 kn downwards D) 2.51 kn upwards E) 1.71 kn upwards 17) 18) A 60.0-kg man stands at one end of a 20.0-kg uniform 10.0-m long board. How far from the man is the center of mass of the man-board system? A) 5.00 m B) 7.50 m C) 9.00 m D) 2.50 m E) 1.25 m 18) 19) A merry-go-round spins freely when Janice moves quickly to the center along a radius of the merry-go-round. It is true to say that (define the system as the merry-go-round + Janice) A) the moment of inertia of the system decreases and the angular speed decreases. B) the moment of inertia of the system decreases and the angular speed remains the same. C) the moment of inertia of the system increases and the angular speed increases. D) the moment of inertia of the system decreases and the angular speed increases. E) the moment of inertia of the system increases and the angular speed decreases. 19) 20) A solid cylinder is rolling without slipping. What fraction of its kinetic energy is rotational? (take I = 1/2 MR2) A) 2/3 B) 1/2 C) 1/4 D) 1/3 E) 3/4 20) 5

6 Answer Key Testname: SPRING2015_EXAM2 1) D 2) C 3) B 4) C 5) B 6) B 7) B 8) A 9) B 10) A 11) B 12) D 13) E 14) A 15) A 16) C 17) D 18) E 19) D 20) D 6