The watt is a rate, similar to something like speed (miles per hour) and other time-interval related measurements.
Specifically, watt means Joules per Second. We are given that the electrical engine has 400 watts, meaning it can make 400 joules per second. If we need 300 kJ, or 3000 Joules, then we can write an equation to solve the time it would take to reach this amount of joules:
w * t = E
w: Watts
t: Time
E: Energy required
(Watts times time is equal to the energy required)
<u>Input our values:</u>
400 * t = 3000
(We need to write 3000 joules instead of 300 kilojoules, since Watts is in joules per second. It's important to make sure your units are consistent in your equations)
<u>Divide both sides by 400 to isolate t:</u>
<u /> =
t = 7.5 (s)
<u>It will take 7.5 seconds for the 400 W engine to produce 300 kJ of work.</u>
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If you have any questions on how I got to the answer, just ask!
- breezyツ