Chapter 6, Problem 2PCE

Predict/Explain Two drivers traveling side-by-side at the same speed suddenly see a deer in the road ahead of them and begin braking. Driver 1 stops by locking up his brakes and screeching to a halt; driver 2 stops by applying her brakes just to the verge of locking, so that the wheels continue to turn until her car comes to a complete stop. (a) All other factors being equal, is the stopping distance of driver 1 greater than, less than, or equal to the stopping distance of driver 2? (b) Choose the best explanation from among the following:

1. I.            Locking up the brakes gives the greatest possible braking force.
2. II.            The same tires on the same road result in the same force of friction.
3. III.            Locked-up brakes lead to sliding (kinetic) friction, which is less than rolling (static) friction.