Physics question.

[Waania]

the input power to a motor is 12w the motor wastes 590 j of energy in 1 min what is the efficiency?
the answer is 18. can someone explain how?

 

[PlanetMaster]

the input power to a motor is 12w the motor wastes 590 j of energy in 1 min what is the efficiency?
the answer is 18. can someone explain how?

Effeciency is output power over input power.

The input power is 12w.

And since the motor "wastes" 590j of energy in 1 min, the power "wasted" can be calculated with
[imath]E=P \times t[/imath]
[imath]P = \frac{E}{t} = \frac {590}{60} = 9.83[/imath]

So output power is [imath]12-9.83 = 2.17[/imath]

And thus,
[imath]Effeciency = \frac{output power}{input power} \times 100 = \frac{2.17}{12} \times 100 = 18%[/imath]