Power

[pm1]

Just to verify...

Measurements of which of the following would be sufficient to calculate the usable work performed by a mechanical engine?
A) The rate at which energy is consumed by the engine and the amount of time the engine
was running
B) The heat produced by the engine and the amount of time the engine was running
C) The power output of the engine and the amount of time the engine was running
D) The energy consumed by the engine and the amount of time the engine was running

Answer:C

I was debating between A and C.
What is the difference between A and C? Is A wrong because of the possibility that the machine doesn't have 100% efficiency??

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[chiddler]

That was my thought. A says nothing about the efficiency. So C is a better answer.

 

[SaintJude]

I think the question is trying to make sure you understand efficiency, yeah? efficiency = useful worked performed by machine / energy it takes in

Choice A speaks only about how much energy the engine it is consuming Does it tell us what percentage of all of the energy "received" get converted into usable energy? No.
So, just by the information given by choice A, we can't really say anything about the engine's efficiency b/c we don't know how the ratio " energy out/ energy used"

edit: oops, didn't see chiddler's post!

 

[pm1]

okay! Thanks guys!