When an automobile moves with constant velocity, the power developed is used to overcome the frictional forces exerted by the air and the road. If the engine develops 30 hp, what total frictional force acts on the car at 140 mph? One horsepower equals 746 W, and one mile is 1609 m. Answer in units of N.

Explanation:

Given:

Power, p = 30 hp

1 hp = 746 W

= 22.38 kW

Velocity, v = 140 mph

1 mile = 1609 m

Converting mph to m/s,

140 mile/hour × 1609 m/1 mile × 1 hour/3600 s

= 62.572 m/s

Summation of forces = 0

Power, p = energy/time

Energy = force × distance;

Velocity = distance/time;

Power = force × velocity

Force, fr = 22380/62.572

= 357.67 N

Frictional force, fr = 0.358 kN.