# Exam 4 Target 1 Retake Preap 16-17

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• 1.

### A painter lifts a bucket of paint, carries it 5 m horizontally then sets it back down. Which of the following is true?

• A.

A. The force of gravity does negative work when the worker lifts the bucket.

• B.

B. The painter does positive work on the bucket when carrying it horizontally at constant speed.

• C.

C. The painter does positive work on the bucket when setting it down.

A. A. The force of gravity does negative work when the worker lifts the bucket.
Explanation
When the painter lifts the bucket of paint, they are exerting an upward force against the force of gravity. Since the displacement is in the same direction as the force applied, the work done by the painter is positive. However, the force of gravity is acting in the opposite direction to the displacement, so it does negative work on the bucket. Therefore, option a is correct.

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• 2.

### If the sign of work is negative,

• A.

A. the force is in the same direction as the displacement.

• B.

B. the force is perpendicular to the displacement.

• C.

C. the component of the force that does work is in the direction opposite the displacement.

• D.

D. the component of the force that does work is perpendicular to the displacement.

C. C. the component of the force that does work is in the direction opposite the displacement.
Explanation
When the sign of work is negative, it indicates that the work done by the force is in the opposite direction of the displacement. This means that the component of the force that actually performs work is acting against the displacement, rather than in the same direction or perpendicular to it. Therefore, option c is the correct explanation.

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• 3.

### A parachutist falls at a constant speed for 200 m. Which of the following is true?

• A.

A. The force of gravity is the only force doing work on the parachutist.

• B.

B. Air resistance is the only force doing work on the parachutist.

• C.

C. No forces are doing work on the parachutist.

• D.

D. No net work is done on the parachutist.

D. D. No net work is done on the parachutist.
Explanation
When a parachutist falls at a constant speed, it means that the forces acting on the parachutist are balanced. Gravity pulls the parachutist downwards, while air resistance pushes against the motion, opposing the force of gravity. Since the parachutist is falling at a constant speed, the forces of gravity and air resistance are equal and opposite, resulting in no net force. When there is no net force, no work is done on the parachutist because work is defined as the product of force and displacement in the direction of the force. Therefore, the correct answer is d. No net work is done on the parachutist.

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• 4.

### In which of the following sentences is work used in the scientific sense of the word?

• A.

a. Holding a heavy box requires a lot of work.

• B.

b. A scientist works on an experiment in the laboratory.

• C.

c. Sam and Rachel pushed hard, but they could do no work on the car.

• D.

d. John learned that shoveling snow is hard work.

C. c. Sam and Rachel pushed hard, but they could do no work on the car.
Explanation
In the scientific sense of the word, work is defined as the exertion of force over a distance. In sentence c, Sam and Rachel pushed hard, but they could do no work on the car because no force was exerted over a distance. This aligns with the scientific definition of work.

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• 5.

### Work is done when

• A.

A. the displacement is not zero.

• B.

B. the displacement is zero.

• C.

C. the force is zero.

• D.

D. the force and displacement are perpendicular.