Exam #3 Name 1) A 2000. kg car, traveling to the right at 30. m/s, collides with a brick wall and comes to rest in 0.20 s. 1) The average force the car exerts on the wall is A) 60. kn. B) 12. kn. C) 300 kn. D) 30. kn. E) 600 kn. 2) Daisy (50. kg mass) skates on ice at 4.0 m/s to greet her friend (70. kg mass), who is standing still, 2) with open arms. As they collide, while holding each other, with what speed do they both move off together? A) 1.7 m/s B) 5.0 m/s C) zero D) 2.5 m/s 3) Car A (mass = 1000 kg) moves to the right along a level, straight road at a speed of 6.0 m/s. It 3) collides directly with car B (mass = 200 kg) in a completely inelastic collision. What is the momentum after the collision if car B was initially at rest? A) 6.0 KN-s to the right B) zero C) 2.0 KN-s to the right D) 8.0 KN-s to the left E) 10. KN-s to the right 4) James moves in a circular path (radius 15.0 m) with a speed of 60.0 m/s. His ANGULAR VELOCITY 4) is A) 120. rev/s. B) 120/ radians/s. C) 120 radians/s. D) 120 radians/s. E) 120/ rpm. 5) A fan blade, whose diameter is 1.0 m, is turning with an angular velocity of 2.0 rad/s. What is the 5) tangential velocity of a point on the tip of the blade? A) 1.0 m/s B) 2.0 m/s C) 5.0 cm/s D) 0.50 m/s E) 1.5 m/s 6) A pulsar (a rotating neutron star) emits pulses at a frequency of 0.40 khz. The period of its rotation 6) is A) 25 ms. B) 2.5 s. C) 0.025 s. D) 0.25 s. E) 2.5 ms. 1
7) What is the angular speed of a record that rotates at 33-1/3 rpm? 7) A) 2.77 rad/s B) 1.74 rad/s C) 3.49 rad/s D) 33.3/ rad/s E) 33.3 rad/s 8) A space station of diameter 40. meters is turning about its axis at a constant rate. What is the period 8) of revolution of the space station if the outer rim experiences an acceleration of 2.5 m/s2? A) 13. s B) 10. s C) 14. s D) 11. s E) 18. s 9) A jet plane flying 600. m/s experiences an acceleration of 4.0 g when pulling out of the dive. What is 9) the radius of curvature of the loop in which the plane is flying? A) 9.2 km B) 5.8 km C) 1.2 km D) 0.64 km E) 7.0 km 10) A boy and a girl are balanced on a massless seesaw. The boy has a mass of 60 kg and the girl's mass 10) is 50 kg. If the boy sits 1.5 m from the pivot point on one side of the seesaw, where must the girl sit on the other side for equilibrium? A) 2.5 m B) 3.0 m C) 1.8 m D) 1.2 m E) 1.3 m 11) A wheel of moment of inertia of 5.00 kg-m2 starts from rest and accelerates under a constant 11) torque of 3.00 N-m for 8.00 s. What is the wheel's rotational kinetic energy at the end of 8.00 s? A) 78.8 J B) 122.0 J C) 57.6 J D) 64.0 J E) 91.9 J 12) A hoop of radius 0.50 m and a mass of 0.20 kg is released from rest and allowed to roll down an 12) inclined plane. How fast is it moving after dropping a vertical distance of 3.0 m? A) 6.2 m/s B) 2.2 m/s C) 5.4 m/s D) 3.8 m/s E) 7.7 m/s 13) A proton of mass M rotates with an angular speed of 2 106 rad/s in a circle of radius 0.80 m in a 13) cyclotron. What is the orbital angular momentum of the proton? (M = 1.67 10-27 kg) A) 2.1 10-21 N-m-s B) 1.1 10-20 N-m-s C) 3.9 10-21 N-m-s D) 2.9 10-21 N-m-s E) 5.3 10-21 N-m-s 14) An object's angular momentum changes by 10 kg-m2/s in 2.0 s. What magnitude average torque 14) acted on this object? A) 10 N-m B) 2.5 N-m C) 20 N-m D) 5 N-m E) 40 N-m 2
TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 15) When a rigid body rotates about a fixed axis all the points in the body have the same linear 15) displacement. 16) Consider a rigid body that is rotating. Which of the following is an accurate statement? 16) A) Its center of rotation must be at rest, i.e., not moving. B) Its center of rotation is its center of gravity. C) All points on the body are moving with the same linear velocity. D) Its center of rotation must be moving with a constant velocity. E) All points on the body are moving with the same angular velocity. 17) What condition or conditions is/are necessary for static equilibrium? 17) A) Fx = 0, Fy = 0 B) Fx = 0, Fy = 0, = 0 C) = 0 D) Fx = 0 E) Fy = 0 18) A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward 18) so that they are one-half their original distance from the pivot point, what will happen to the seesaw? A) Nothing, the seesaw will still be balanced. B) The side the girl is sitting on will tilt downward. C) The side the boy is sitting on will tilt downward. D) It is impossible to say without knowing the masses of the children. E) It is impossible to say without knowing the values of the original distances. 19) Consider a solid object which is subjected to a net torque. That object will experience which of the 19) following? A) a changing moment of inertia B) an angular acceleration C) a constant angular velocity D) a linear acceleration and an angular acceleration 3
20) A ball, solid cylinder, and a hollow pipe all have equal masses and radii. If the three are released 20) simultaneously at the top of an inclined plane, which will reach the bottom first? A) cylinder B) ball C) they all reach bottom in the same time D) pipe 21) Angular momentum cannot be conserved if 21) A) the angular displacement changes. B) there is net torque on the system. C) the moment of inertia changes. D) there is a net force on the system. E) the angular velocity changes. 22) An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. 22) What happens to his moment of inertia about the axis of rotation? A) It changes, but it is impossible to tell which way. B) It decreases. C) It does not change. D) It increases. 23) Two cars suffer a head-on collision. What is conserved in the collision? 23) A) momentum B) kinetic energy C) mechanical energy and momentum D) (Neither energy nor momentum is conserved.) 24) A sailboat of mass m is moving with a momentum p. Which of the following represents its kinetic 24) energy? A) p2/2m B) mp C) 1/2 mp2 D) mp/2 E) mp/3 25) A car hits another and the two bumpers lock together during the collision. Is this an elastic or 25) inelastic collision? A) inelastic B) insufficient information (It could be either.) C) elastic 4
26) In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with 26) the same velocity as the cue ball had originally. The type of collision is A) elastic. B) elastic or inelastic, depending on the mass of the balls. C) inelastic. D) completely inelastic. 27) A 100 kg football linebacker moving at 2 m/s tackles head-on an 80 kg halfback running 3 m/s. 27) Neglecting the effects due to digging in of cleats A) neither player will drive the other backward. B) this is a simple example of an elastic collision. C) the halfback will drive the linebacker backward. D) the linebacker will drive the halfback backward. 28) Two equal mass balls (one blue and the other gold) are dropped from the same height, and 28) rebound off the floor. The blue ball rebounds to a higher position. Which ball is subjected to the greater magnitude impulse during its collision with the floor? A) It's impossible to tell since the time intervals and forces are unknown. B) the blue ball C) Both balls were subjected to the same magnitude impulse. D) the gold ball TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 29) In an inelastic collision, the initial kinetic energy is less than the final kinetic energy. 29) 30) Which of the following has units of momentum? 30) A) kg-s/m B) kg-m2/s C) J-s/m D) kg-m2/s2 E) N-m 31) Automobile air bags reduce what during a collision? 31) A) speed of the automobile B) the impulse exerted upon the passenger C) the forces exerted upon the passenger D) the kinetic energy transferred to the passenger 5
32) A 1200. kg ferryboat is moving south at 20. m/s. Its momentum is 32) A) 2.4 103 kg m/s B) 24. kn s C) 1.7 10-3 N s D) 1.2 103 kg m/s E) 6.0 102 kg m/s 33) A handball of mass 0.10 kg, traveling horizontally at 25. m/s, strikes a wall and rebounds at 19. m/s. 33) What is the change in the momentum of the ball? A) 72 N-s B) 4.4 N-s C) 5.4 N-s D) 1.8 N-s E) 1.2 N-s 34) Car A (mass = 1000 kg) moves to the right along a level, straight road at a speed of 6.0 m/s. It 34) collides directly with car B (mass = 200 kg) in a completely inelastic collision. What is the speed of the car immediately after the collision? A) 5.0 m/s B) zero C) 6.0 m/s D) 4.0 m/s E) 3.0 m/s 35) When a light beach ball rolling with a speed of 6 m/s collides with a heavy exercise ball at rest, the 35) beach ball's speed after the collision will be approximately A) 18 m/s. B) 3 m/s. C) 12 m/s. D) 6 m/s. E) 0. TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 36) When a rigid body rotates about a fixed axis all the points in the body have the same angular 36) speed. 37) Moment of Inertia has which of the following units? 37) A) kg m2 / s B) J C) N m D) kg m2 E) kg m2 / s2 38) A solid cylinder and a hollow cylinder have the same mass and the same radius. Which statement 38) is true concerning their moment of inertia about an axis through the exact center of the flat surfaces? A) The solid cylinder has the greater moment of inertia. B) The hollow cylinder has the greater moment of inertia. C) Both cylinders have the same moment of inertia. D) The moment of inertia cannot be determined since it depends on the amount of material removed from the inside of the hollow cylinder. 6
39) An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. 39) What happens to his rotational kinetic energy about the axis of rotation? A) It decreases. B) It does not change. C) It increases. D) It changes, but it is impossible to tell which way. 40) A bicycle is moving 4.0 m/s. What is the angular speed of a wheel if its radius is 30.cm? 40) A) 1.2 rad/s B) 4.8 rad/s C) 7.6 rad/s D) 0.36 rad/s E) 13. rad/s 41) A potter's wheel with a moment of inertia of 8.0 kg-m2 has 5.0 N-m applied to it. It starts from 41) rest. 10. s later it has gained what kinetic energy? A) 0.12 kj B) 1.6 kj C) 44. J D) 53. J E) 78. J 42) An 8.0 kg-m2 wheel with 155. Joules of rotational kinetic energy requires what torque to bring it to 42) rest in 4.0 s? A) +0.88 N-m B) -1.8 N-m C) -1.2 N-m D) -1.6 N-m E) -1.0 N-m 43) Rotational Kinetic Energy has which of the following units? 43) A) kg m / s2 B) J C) J m D) N m2 E) kg m2 / s 44) What condition or conditions is/are necessary for rotational equilibrium? 44) A) Fx = 0, Fy = 0 B) Fx = 0, Fy = 0, = 0 C) Fx = 0 D) = 0 E) Fy = 0 45) "Lever Arm" can have which of the following units? 45) A) N m2 B) kg m2 / s C) J D) kg m / s2 E) m 7
46) The condition for rolling without slipping is that the center of mass speed is 46) A) Vcm = r B) Vcm= r 2 C) Vcm = 2 r D) Vcm = r / 2 E) Vcm = r2 TRUE/FALSE. Write 'T' if the statement is true and 'F' if the statement is false. 47) Unbalanced torques produce rotational accelerations, and balanced torques produce rotational 47) equilibrium. 48) A 2.0 kg mass moving to the East at a speed of 4.0 m/s collides head-on in an inelastic collision 48) with a stationary 2.0 kg mass. How much kinetic energy is lost during this collision? A) zero B) 16. J C) 8.0 J D) 2.0 J E) 4.0 J 49) A 3. kg ball of putty moving at 1 m/s collides and sticks to a 2 kg ball initially at rest. The putty and 49) ball then move with a momentum of A) 0 N-s. B) 4 N-s. C) 3 N-s. D) 2 N-s. E) 1 N-s. 50) A 2.0 kg softball is pitched to you at 20. m/s. You hit the ball back along the same path, and at the 50) same speed. If the bat was in contact with the ball for 0.10 s, the average force the bat exerted was A) zero. B) 0.65 kn. C) 40. N. D) 0.40 kn. E) 0.80 kn. 8