An automobile is moving at `100 kmph` and is exerting attractive force of `3920 N`. What horse power must the engine develop, if `20 %` of the power developed is wasted ?

Explanation

Velocity = `100 kmph = 100 xx 5/18 m/s` Force = 3920 N Useful power = 80%
Power `= W/t = F.S/t = F.v` `Rightarrow 80/100P = 3920 xx 100 xx5/18`
`P = 100/80 xx 3920 xx 100 xx 5/18`
` = 13.16 xx 10^(4)W = 182.5 hp`.