Braking Distance


Braking a Truck Problem Animation

Here is some braking-distance data.

You might want to compare the following solution with the

A Solution:

The kinetic energy of the truck is given by:

KE = (1/2)mv^2

so if you double the speed of the truck, you give it 4 times the kinetic energy.

According to the work-energy equation:

(Work done by the net force equals the change in the object's kinetic energy) in order to stop the truck when it is going twice as fast, the brakes of the truck must do 4 times the work as before.

If the force exerted by the brakes is more-or-less constant, then:

work done by the brakes = -(force)(distance).

Assuming that the brakes can exert the same maximum force regardless of the speed of the truck (which is reasonable), the braking distance must be 4 times as much (48 meters) if the speed is doubled.

last update May 21, 1999 by JL Stanbrough