Energy, Work, and Power Flashcards

A 200-pound crate is pushed 15 feet along a level floor. How much work is done against gravity?

Answer: 0 ft-lb

No work is done against gravity when an object moves horizontally, since gravity acts vertically.

Which of the following best describes potential energy?

Answer: Stored energy due to position or condition

Potential energy is stored energy that an object has due to its position, shape, or condition.

How much work is done when a 300 lb engine block is lifted 4 feet onto a workbench?

Answer: 1,200 ft-lb

Work = Force × Distance = 300 lb × 4 ft = 1,200 ft-lb.

A motor lifts a 500 lb load 10 feet in 5 seconds. What is the power output?

Answer: 1,000 ft-lb/s

Power = (Force × Distance) / Time = (500 × 10) / 5 = 1,000 ft-lb/s.

Two workers each move identical boxes up the same flight of stairs. Worker A takes 10 seconds; Worker B takes 20 seconds. Which statement is true?

Answer: Both do the same work but A uses more power

Work depends only on force and distance, so both do the same work, but Worker A uses more power because she completes it in less time.

A compressed spring is an example of which type of energy?

Answer: Elastic potential energy

A compressed spring stores elastic potential energy, which is released when the spring returns to its natural length.

One horsepower is equal to which of the following?

Answer: Both 550 ft-lb/s and 33,000 ft-lb/min

One horsepower equals 550 ft-lb/s, which is equivalent to 33,000 ft-lb/min (550 × 60).