Power is the rate at which work is done.

• A. False
• B. Sometimes
• C. True
• D. Never

Answer: (C)

Power is the rate at which work is done. Work is the energy transferred when a force moves an object through a distance in the direction of the force, and power tells you how quickly that transfer happens. So power equals work divided by time: P = W/t. Since work can be expressed as F·d and velocity is d/t, power can also be written as P = F·v. The standard unit is the watt, which is one joule per second.

If you do the same amount of work in less time, power increases; if you take longer, power decreases. For example, lifting a 20-newton weight by 2 meters in 1 second does 40 joules of work, so the power is 40 watts. If you do the same lift in 4 seconds, the power is only 10 watts. Remember, energy is the total amount transferred, while power is how quickly that transfer occurs.