An electric motor operator on `15 V` supply, draws a current of `5 A` and yields mechanical power of `60 W`. The energy lost as heat in one hour (in kJ) is.

Options

A. `0.54`
B. `5.4`
C. 54
D. 540

Answer

C

Explanation

`V = 15 V, I = 5 A, P = 60 W, t = 1 h = 3600 sec`.
Power supplied `= VI = 15 xx 5 = 75 W`
Mechaical power yielded `P = 60 W`
Power lost = power lost `= 75 - 60 = 15 W`
Energy lost = Power lost `xx` time
`= 15 xx 3600 = 54000 J = 54 kJ`