A motor cycle engine delivers a power of `10 kW`, by consuming petrol at the rate of `2.4 kg//hour`. If the calorific value of petrol is `35.5 MJ//kg`, the rate of heat rejection by the exhaust by

Options

A. `5.5 kW`
B. `13.7 kW`
C. `11.2 kW`
D. `9.7 kW`

Answer

B

Explanation

Heat recived (or produce by the burning of petrol) in one hour will be
`=(2.4 kg//hour) (3.5 MJ//kg)`
`=85.2xx10^(6)J//hour`
`:.` The rate at which heat is recevied ltbr. `=(85.2xx10^6 J)/((3600s)) = 2.37xx10^(4) J//s = 23.7kW`
Evidently the rate of heat rejection
=rate at which heat is produced - rate at which work is obtained = `23.7kW - 10kW = 13.7kW`.