Question

An engine accelerate a car of mass `800 kg` to a speod of `72 km//h`. If the frictional force is `10 N` per tonne, the power developed by the engine is:
A. `10 kW`
B. `15 kW`
C. `20 kW`
D. `5 kW`

Answer 1

Correct Answer - D
Speed of car , `v = 72km//h= 72 xx (5)/(18) = 20ms^(-1)`
`KE = (1)/(2)mv^(2) = (1)/(2) xx 800 xx 400 = 400 xx 400 J`
`P = (KE)/(Time)= (400 xx 400)/(32) = 5000 W = 5 kW`