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Using a flywheel in a hybrid car

Engineer Elizabeth likes the idea of hybrid cars, but doesn't like batteries. She decides to store energy with a flywheel: a flat circular disk of steel, with diameter D = 1 m and height h.

Her car has a total mass of M = 1500 kg. Elizabeth plans on transferring kinetic energy from the car to the flywheel as the car slows down, then restoring it from the flywheel to get the car going after a stop. She comes up with a rough design: make the flywheel able provide the energy needed to accelerate the car from rest to v = 20 mph. The maximum angular velocity allowed by the car's frame is omega = 400 rpm.

  1. How much rotational KE must the flywheel store?
  2. What should the height h of the flywheel be? (Hint: see page 317)

    3. (if you have time)

  3. Is this idea practical? What fraction of the car's total mass is the flywheel alone?

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