Ch.9 PHYSICS FINAL

9.5.1. An object is rolling, so its motion involves both rotation and translation. Which one of the following statements must be true concerning this situation? a) The total mechanical energy is equal to the sum of the translational and rotational kinetic energies plus the gravitational potential energy of the object. b) The translational kinetic energy may be equal to zero joules.c) The gravitational potential energy must be changing as the object rolls. d) The rotational kinetic energy must be constant as the object rolls. e) The total mechanical energy is equal to the sum of the translational kinetic energy and the gravitational potential energy of the object.

a) The total mechanical energy is equal to the sum of the translational and rotational kinetic energies plus the gravitational potential energy of the object.

Which one of the following statements most accurately describes the center of gravity of an object? a) It is the point on the object where all the weight is concentrated. b) It is the point from which the torque produced by the weight of the object can be calculated. c) It must be experimentally determined for all objects. d) It is the point where gravity acts on the object. e) It is the point where all the mass is concentrated.

b) It is the point from which the torque produced by the weight of the object can be calculated.

9.1.3. A unit of torque is which of the following? a) newtons (N) b) N x m c) kg/s2 d) kg x m2 e) angular newtons (aN)

b) N x m

9.6.2. A child standing on the edge of a freely spinning merry-go-round moves quickly to the center. Which one of the following statements is necessarily true concerning this event and why? a) The angular speed of the system decreases because the moment of inertia of the system has decreased. b) The angular speed of the system increases because the moment of inertia of the system has decreased. c) The angular speed of the system increases because the moment of inertia of the system has increased. d) The angular speed of the system decreases because the moment of inertia of the system has increased. e) The angular speed of the system remains the same because the net torque on the merry-go-round is zero N x m.

b) The angular speed of the system increases because the moment of inertia of the system has decreased.

9.2.3. Complete the following statement: When determining the net torque on a rigid body, only the torques due to a) internal forces are considered. b) external forces are considered. c) only forces that are either parallel or perpendicular to the lever arm are considered. d) forces that form action-reaction pairs as in applying Newton's third law of motion are considered. e) both internal and external forces are considered.

b) external forces are considered.

9.6.4. The moment of inertia of a wheel about its axle does not depend on which one of the following properties? a) the mass of the wheel b) the diameter of the wheel c) the angular velocity of the wheel as it rotates d) the location of the particles that compose the wheel

c) the angular velocity of the wheel as it rotates

9.1.2. A force is applied to a doorknob. This force will be most effective in causing the door to rotate when which of the following is true? a) The lever arm is parallel to the direction of the force. b) The lever arm length is zero meters. c) The direction of the force is at an angle of 45 degrees with respect to the door. d) The direction of the force is at an angle of 90 degrees with respect to the door. e) The lever arm is perpendicular to the door.

d) The direction of the force is at an angle of 90 degrees with respect to the door.

9.2.5. A water skier is pulled by a boat traveling with a constant velocity. Which one of the following statements is false concerning this situation? a) The water skier is in equilibrium. b) The net acceleration of the skier is zero m/s2. c) The net force on the skier is zero newtons. d) There is a net horizontal force on the skier in the direction the boat's velocity. e) The net vertical force on the skier is zero newtons.

d) There is a net horizontal force on the skier in the direction the boat's velocity.

9.1.1. Which one of the following choices is produced when a constant net torque is applied to a rigid object? a) a constant linear acceleration of the object b) a constant angular velocity of the object c) a rotational equilibrium of the object d) a change in the angular velocity of the object e) a constant angular displacement of the object

d) a change in the angular velocity of the object

9.4.3. An object, which is considered a rigid body, is not in equilibrium. Which one of the following statements must be true concerning the magnitude of the angular acceleration ⍺ translational acceleration a of the object? a) ⍺=0rad/s2 and a=0m/s2 b) ⍺> 0rad/s2 but a=0m/s2 c) a>0m/s2 but ⍺= 0rad/s2 d) ⍺> 0rad/s2 and a>0m/s2 e) Either⍺>0rad/s2 or a>0m/s2

e) Either⍺>0rad/s2 or a>0m/s2

9.6.3. What happens when a spinning ice skater draws in her outstretched arms? a) Her moment of inertia decreases causing her to slow down. b) Her angular momentum decreases. c) The torque that she exerts increases her moment of inertia. d) Her angular momentum increases. e) Her moment of inertia decreases causing her to spin faster.

e) Her moment of inertia decreases causing her to spin faster.

9.2.1. Which one of the following descriptions indicates that the object is in translational equilibrium? a) Translational equilibrium occurs only if the object is at rest. b) Translational equilibrium occurs only if the object is moving with constant acceleration. c) Translational equilibrium occurs only if the object is at moving with constant (but not zero) velocity. d) Translational equilibrium occurs if the object is moving with constant velocity or with constant acceleration. e) Translational equilibrium occurs if the object is at rest or moving with constant velocity.

e) Translational equilibrium occurs if the object is at rest or moving with constant velocity.