An 800-kg car traveling in a straight line at a speed of 30 m/s applies its brakes.During braking,there is a net force of 2000 N in the horizontal direction on the car.What distance will the car move from the time it applies its brakes until it has stopped?
A)12 m
B)75 m
C)180 m
D)300 m
E)60,000 m

Question

Quizplus · Accepted Answer

Using the work-energy principle, the work done by the brakes (force times distance) equals the change in kinetic energy. The initial kinetic energy is (1/2)mv^2 = (1/2)(800 kg)(30 m/s)^2 = 360,000 J. The work done by the brakes is force times distance, 2000 N * d. Setting these equal gives 2000d = 360,000, so d = 180 m.

An 800-Kg Car Traveling in a Straight Line at a Speed