# Mechanics: Multiple Choice Questions

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1. An offensive lineman weighs twice what you weigh, and has three times your arm strength. You are trying to push him out of the way. The magnitude of the force he exerts on you will be:

A. six times the force you exert on him.

B. three times the force you exert on him.

C. twice the force you exert on him.

D. the same as the force you exert on him.

2. When catching a ball:

A. the ball performs positive work on the glove and the glove performs negative

work on the ball.

B. the ball performs negative work on the glove, and the glove performs positive work on the ball.

C. positive work is performed on both the ball and the glove.

D. no work is performed on either the ball or the glove.

3. The kinetic energy of a baseball traveling at 80 mph, compared to the same ball traveling at 40 mph, is:

A. twice. B. four times. C. half. D. None of the above.

4. A pitcher exerts an average horizontal force of 60 N against a baseball while moving it through a horizontal displacement of 2.0 m before he releases it. The horizontal velocity the ball acquires is 40 m/s. If the pitcher were to exert only 30 N, how much horizontal displacement of the ball would be needed for it to acquire the same horizontal

velocity?

A. 1.0 m. B. 2.0 m. C. 4.0 m. D. 30 m.

5. Bill lifts a 1000 N barbell 1.5 m in 1 second, while Bob lifts a 1400 N barbell 2.0 m in 2 seconds. Whose average power output is greater?

A. Bill's B. Bob's. C. They are equal. D. Who cares.

6. The moment arm of a muscle is:

A. the distance from the joint to the point where the nearest tendon attaches to bone.

B. the distance from the joint to the point where the farthest tendon attaches to bone.

C. muscle length × tan(joint angle).

D. None of the above.

7. The weight of your forearm, hand, and an additional weight is 50 N, and this total weight, which tries to extend your elbow, has a moment arm of 20 cm about the elbow joint. The biceps is the only muscle in the elbow which is contracting, its force being 500 N. The moment arm of the biceps is 2 cm. What is the net torque about the elbow?

A. 500 N.m.

B. 10 N.m.

C. Zero.

D. Can not be determined from the information provided.

8. Three forces act on an object, whose resultant is not zero. If the net torque due to the three forces is zero, then:

A. equilibrium is possible.

B. the object will spin at an increasing rate.

C. the object will accelerate.

D. None of the above.

9. In equilibrium, muscle force is usually much larger in magnitude than the external force on a body segment. The net force on the segment is nevertheless zero because:

A. the net torque due to the external and muscle forces is zero.

B. there are contact forces at joints.

C. gravitational forces should not be included in equilibrium conditions.

D. muscle moment arms are small.

#### Solution Preview

1. By Newton's third law of motion, the forces of action and reaction are equal and opposite. The pushing force exerted on the lineman being the action, the lineman will exert an equal and opposite force on the pusher.

2. The ball pushes against the glove and its kinetic energy is lost in the process. The glove being cushioned, gets compressed. Hence, the force exerted by the ball results in displacement of the glove in the same direction. Hence, positive work is done by the ball on ...

#### Solution Summary

The following posting helps with problems involving mechanics. Step by step calculations are provided for each.