The driver of a truck suddenly hits the brake pedal while it

The driver of a truck suddenly hits the brake pedal while it is traveling at 30 fps, and the truck comes to rest without skidding because it is equipped with an ABS. The truck weighs 4000 lb, the dynamic and static coefficients of friction between the tires and the road are 0.25 and 0.3, respectively. Determine the magnitude of the frictional force exerted by the ground on the truck.

Solution

The frictional forces are enough to prevent skidding, so only static friction comes into play.

The frictional force is = Mu*N where N is the normal force and Mu the coefficient of friction

Substituting, the force comes to 1200 lb mass or 38640 lbft/s*s pound force.