Question

An automobile engine with an efficiency 0.30 dumps heat to the environment at the rate of 280 kW .

What's its mechanical power output in W ?

What's its mechanical power output in hp ?

Answer 1

Energy given out by the engine per second, Qout = 280 kJ

let Qin is Energy taken by the engine per second.

we know, efficiency, n = 1 - Qout/Qin

Qout/Qin = 1 - n

Qout/Qin = 1 - 0.3

Qout/Qin = 0.7

Qin = Qout/0.7

= 280*10^3/0.7

= 400*10^3 J in one second

Workdone by the engine in one second = Qin - Qout

= 400*10^3 - 280*10^3

= 120*10^3 J

so, mechanical power output = 120*10^3 W or 120 kW <<<<<<----------------Answer

mechanical power output = 120*10^3/(746) hp

= 160.86 hp <<<<<<----------------Answer