Free Power MCQs with Answers

1. Power is correctly defined as

• A. the total work done
• B. the rate of doing work
• C. work done times time taken
• D. force times displacement

Explanation: Power is work done per unit time, measured in watts, where one watt is one joule per second. For a body moving at constant velocity it can also be written as force times velocity. Force times displacement is work itself, not the rate at which it is done.

2. A pump raises 200 kg of water through 10 m in 20 s. Taking g as 10 m s-2, its output power is

• A. 100 W
• B. 1000 W
• C. 2000 W
• D. 20000 W

Explanation: The work done is mgh, which is 200 times 10 times 10, giving 20000 J. Dividing by the 20 s taken gives 1000 W, or 1 kW. Forgetting to divide by time leaves the answer at 20000, which is the energy in joules rather than the power in watts.

3. Power is defined as

• A. the total work done
• B. the rate at which work is done or energy is transferred
• C. the force multiplied by the distance
• D. the energy stored in a body

Explanation: One watt is one joule per second, so power tells you how quickly energy is delivered rather than how much. Two motors may do the same work while one takes half the time and therefore has twice the power. Power can also be written as force multiplied by velocity when the force is constant.

4. A pump raises 100 kg of water through 10 m in 20 seconds. Taking g as 10 m per second squared, its power output is

• A. 500 W
• B. 1000 W
• C. 200 W
• D. 10000 W

Explanation: The work done is mgh, that is 100 multiplied by 10 multiplied by 10, giving 10,000 J, and dividing by 20 seconds gives 500 W. Forgetting to divide by the time leaves the 10,000 distractor, which is the energy rather than the power. The pump's input power would be higher than this, since no machine is fully efficient.