When an automobile moves with constant speed down a highway , most of the power developed by the engain is used to compensate on the car by the air and the road, friction forces exerted on the car by the air and the road. If the power developed by an engine is `175 hp`, estimate the total friction force (apporox) acting on the car when it is moving at a speed of `25 m//s`. One horsepower equals `746 W`.

Options

A. `360 kN`
B. `373 kN`
C. `250 kN`
D. `500 kN`

Answer

D

Explanation

When the car moves at constant speed on a level roadway , the power used to veer come the total friction force equal the power input from the engine .
or `P_(output) =f_("total")v=P_(imput)`. This gives
`f_("total")=(P_(imput))/(v) =((175 hp)/(1 hp))`
`5.22xx10^(5) N` or about `5xx10^(5) N` or `500 kN`
(approx.).