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In SI units, the watt is the unit of power. How is one watt related to the joule and the second?
AOne watt equals one joule per second
BOne watt equals one joule times one second
COne watt equals one second per joule
DOne watt equals one joule per square second
Answer & Solution
Correct answer: A. One watt equals one joule per second
1. Power is work divided by time, so its SI unit is a unit of work divided by a unit of time.
2. Work is measured in joules and time in seconds, so the resulting unit of power is joules per second, named the watt.
3. Multiplying joules by seconds, or inverting the ratio to seconds per joule, does not match a rate defined as work divided by time.
4. A joule per square second would instead resemble a rate of change of power, not power itself.
_Source: OpenStax College Physics (CC BY 4.0), Ch 7 "Work, Energy, and Energy Resources", section 7.7 Power_
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