Question

this is a 2 part question2) 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 byapplying 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 thefollowing: 1. Locking up the brakes gives the greatest possible braking force.2. The same tires on thesame road result in the same force of friction.3. Locked-up brakes lead to sliding (kinetic) friction, which is less than rolling (static) friction.

Answer 1

The maximum static friction between two surfaces is greater than the kinetic friction between them.

If the wheels of a car get locked, the surface of the wheel slides through the floor and kinetic friction acts to stop the car.

If the wheels of the car don't get locked, they may turn fast enough to prevent the surface of the wheel from sliding through the floor and static friction acts on the car.

Since the force acting on the car with its wheel locked is less than the force acting on the car with the turning wheels, then, the stopping distance is greater for driver 1 than for diver 2.

Therefore, the answers are:

a) The stopping distance of driver 1 is greater than the stopping distance of driver 2.

b) The best explanation is:

3. Locked-up brakes lead to sliding (kinetic) friction, which is less than rolling (static) friction.