Question

The engine of an automobile develops power of 20 hp when the automobile is travelling at 50km/h. (A) what is the resisting force acting on the automobile if the resisting force is proportional to the velocity? (B) what horsepower will drive the car at 25km/h?

Answer 1

The following relation between power (P), force (F) and velocity (v) exists

P = F.v

now,

(1)

now, F = P/v

here,

P = 20 hp = 14914 W

v = 50 km/hr = 13.9 m/s

so, resistive force

F = 14914 / 13.9

thus,

F = 1073 N

..

(2)

P = F.v

here,

F = 1073

v = 25 km/hr = 6.9 m/s

so,

P = 1073 x 6.9

thus, driving power will be

P = 7403.7 W

or in horse power terms

P = 9.93 hp