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# need an explanation guys . watch

1. in a test of muscle efficiency, an athlete on an exercise bicycle pedals against a brake force of 30N at a speed of 15ms^ .
calculate the useful energy supplied per second by the athlete's muscles?
i know in order to answer the above question you need to multiply 30 by 15 but why would you do that to get the answer?Doest it have any especial formula for it?An explanation would be much appreciated .
2. (Original post by Alen.m)
in a test of muscle efficiency, an athlete on an exercise bicycle pedals against a brake force of 30N at a speed of 15ms^ .
calculate the useful energy supplied per second by the athlete's muscles?
i know in order to answer the above question you need to multiply 30 by 15 but why would you do that to get the answer?Doest it have any especial formula for it?An explanation would be much appreciated .

Power = Force x Velocity

Power is energy per second, or J/s.

3. Does this formula always give you the useful energy?thanks btw
4. (Original post by Alen.m)
Does this formula always give you the useful energy?thanks btw
Power is not energy. It's energy per unit time, or Joule/Second. Useful energy in this case, is just a term used for the question. It's useful energy supplied by the muscles, (it's doing something).
5. (Original post by Alen.m)
Does this formula always give you the useful energy?thanks btw
It just calculates energy expenditure (per unit time, since that's what power is). Quite often it will be energy lost as heat due to friction from a car travelling at constant velocity or a similar scenario (so no, quite a lot of the time it will be calculating waste energy).

Sorry for the mix of words and symbols. Basically if you take the definition of work (W=Fd) and divide through by time you get Power on the left and Fv on the right.

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