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Work and kinetic energy

First, we'll do an example involving linear motion -- then, one with rotational motion.

Consider the Toyota Corolla, which has a mass of m = 1100 kg.


Image of Toyota Corolla courtesy of Toyota

The car is equipped with tires which have a coefficient of kinetic friction μk = 0.85. Its owners drive safely at the speed limit of 55 mph = 24.6 m/s.

  1. What is the initial KE of the car?

Suddenly, a little bunny rabbit hops into the road. The driver slams on the brakes.

  1. How much work will it take to stop the car?
  2. What is the friction force on the car, due to the tires?
  3. How far will the car skid until it stops?

Work in rotational motion

A potter's wheel has mass M = 35 kg and radius 0.8 m. It is initially at rest, but needs to spin at a steady 200 RPM for Polly the Potter to make her bowls.

In order to accelerate the wheel to full speed during just N = 5 revolutions, how much torque must Polly exert on the wheel?

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.