WTMA Energy, Work, and Power 2 — Questions and Answers
Question 1: A 200-pound crate is pushed 15 feet along a level floor. How much work is done against gravity?
- 3,000 ft-lb
- 200 ft-lb
- 0 ft-lb (Correct answer)
- 15 ft-lb
Correct answer: 0 ft-lb
No work is done against gravity when an object moves horizontally, since gravity acts vertically.
Question 2: Which of the following best describes potential energy?
- Energy of motion
- Stored energy due to position or condition (Correct answer)
- Heat released by friction
- Energy lost to sound
Correct answer: Stored energy due to position or condition
Potential energy is stored energy that an object has due to its position, shape, or condition.
Question 3: How much work is done when a 300 lb engine block is lifted 4 feet onto a workbench?
- 75 ft-lb
- 304 ft-lb
- 1,200 ft-lb (Correct answer)
- 12 ft-lb
Correct answer: 1,200 ft-lb
Work = Force × Distance = 300 lb × 4 ft = 1,200 ft-lb.
Question 4: A motor lifts a 500 lb load 10 feet in 5 seconds. What is the power output?
- 500 ft-lb/s
- 1,000 ft-lb/s (Correct answer)
- 2,500 ft-lb/s
- 250 ft-lb/s
Correct answer: 1,000 ft-lb/s
Power = (Force × Distance) / Time = (500 × 10) / 5 = 1,000 ft-lb/s.
Question 5: 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?
- Worker A does more work
- Worker B does more work
- Both do the same work but A uses more power (Correct answer)
- Both do the same work but B uses more power
Correct 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.
Question 6: A compressed spring is an example of which type of energy?
- Kinetic energy
- Thermal energy
- Elastic potential energy (Correct answer)
- Chemical energy
Correct answer: Elastic potential energy
A compressed spring stores elastic potential energy, which is released when the spring returns to its natural length.
Question 7: One horsepower is equal to which of the following?
- 33,000 ft-lb per minute
- 550 ft-lb per second only
- Both 550 ft-lb/s and 33,000 ft-lb/min (Correct answer)
- 1,000 watts
Correct 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).
WTMA Energy, Work, and Power 2
A 200-pound crate is pushed 15 feet along a level floor.
How much work is done against gravity?