A machine does 50 J of work in 5 s. What is its power?

A machine does 50 J of work in 5 s. What is its power?

• A. 5 W
• B. 0.5 W
• C. 20 W
• D. 10 W

Answer: (D)

Power is the rate at which work is done, or energy transferred, so it equals work divided by time. Since 1 watt equals 1 joule per second, you can think of power as how many joules are delivered each second. Here, the machine does 50 joules of work in 5 seconds. Divide: 50 J ÷ 5 s = 10 J/s, which is 10 watts. So the power is 10 W. If you check the other options by imagining different amounts of work in the same time, you’d get: 5 watts would require 25 J in 5 s, 0.5 watts would be 2.5 J in 5 s, and 20 watts would be 100 J in 5 s.

Power is the rate at which work is done, or energy transferred, so it equals work divided by time. Since 1 watt equals 1 joule per second, you can think of power as how many joules are delivered each second.

Here, the machine does 50 joules of work in 5 seconds. Divide: 50 J ÷ 5 s = 10 J/s, which is 10 watts. So the power is 10 W.

If you check the other options by imagining different amounts of work in the same time, you’d get: 5 watts would require 25 J in 5 s, 0.5 watts would be 2.5 J in 5 s, and 20 watts would be 100 J in 5 s.