Question

In a motor the electrical power input is 500 W and the mechanical power output is 0.54 horse power. Heat developed in the motor in 1 h is (assuming that all the electric energy which is not converted to mechanical energy is converted to heat) is
A. `4.18xx10^4cal`
B. `3.6xx10^5cal`
C. `8.6xx10^4cal`
D. `1.28xx10^5cal`

Answer 1

Correct Answer - C
Efficiency`=(0.54xx746)/(500)=0.80` or 80 %
(`0.5kW=500W` and `0.54hp=0.54xx746W`)
`:. 80%` of the electrical energy is converted to mechanical energy and the rest `20%` is converted to heat energy.
`:. (20)/(100)xx500=100W` of power is converted to heat
`:.` Heat produced in 1 h (or 3600s)
`=100xx3600=36xx10^4J`
`=(36xx10^4)/(4.18)cal=8.6xx10^4cal`