WTMA Energy, Work, and Power 5

Question 1

A spring-loaded device stores 500 joules of energy when compressed. If it releases all that energy in 0.1 seconds, what is the average power output?

Accepted Answer

5,000 watts

Answer

Power = Energy / Time = 500 J / 0.1 s = 5,000 watts.

Question 2

On a construction site, a crane lifts a steel beam weighing 2,000 lbs to a height of 30 feet. How much work is done?

Accepted Answer

60,000 ft-lb

Answer

Work = Force × Distance = 2,000 lbs × 30 ft = 60,000 ft-lb.

Question 3

Two identical balls are dropped from different heights. Ball A is dropped from 10 feet; Ball B from 20 feet. Compare their speeds just before hitting the ground.

Accepted Answer

Ball B is about 1.4 times faster than Ball A

Answer

Speed is proportional to the square root of height (v = √(2gh)), so doubling height increases speed by √2 ≈ 1.4 times.

Question 4

Which of the following machines can have an efficiency greater than 100%?

Accepted Answer

No machine can exceed 100% efficiency

Answer

No machine can exceed 100% efficiency because energy cannot be created; some energy is always lost to friction or heat.

Question 5

A worker applies 50 lbs of force at an angle of 90° to the direction of motion. How much work is done?

Accepted Answer

0 ft-lb regardless of distance

Answer

Work = Force × Distance × cos(90°) = F × d × 0 = 0; a perpendicular force does no work.

WTMA - Wiesen Test of Mechanical Aptitude Practice Test

WTMA - Wiesen Test of Mechanical Aptitude Practice Test

WTMA Energy, Work, and Power 5