An experimental flywheel, used to store energy and replace an automobile engine,

Question

An experimental flywheel, used to store energy and replace an automobile engine, is a solid disk of mass 211 kg and radius 0.380 m. What is its rotational inertia? When driving at 20.6 m/s (46.1 mph), the fully energized flywheel is rotating at an angular speed of 3121 rad/s. What is the initial rotational kinetic energy of the flywheel? If the total mass of the car is 1070 kg, find the ratio of the initial rotational kinetic energy of the flywheel to the translational kinetic energy of the car. If the force of air resistance on the car is 650 N, how far can the car travel at a speed of 20.6 m/s (46.1 mph) with the initial stored energy? Ignore losses of mechanical energy due to means other than air resistance.

Explanation / Answer

An experimental flywheel, used to store energy and replace an automobile engine, is a solid disk of mass 211 kg and radius 0.380 m.

What is its rotational inertia?

I = 0.5 m R^2 = 0.5 * 211 * 0.38*0.38 = 15.2342 15.2 Kg.m2

When driving at 20.6 m/s (46.1 mph), the fully energized flywheel is rotating at an angular speed of 3121 rad/s. What is the initial rotational kinetic energy of the flywheel?

0.5 I w^2 = 0.5*15.2342*3121*3121 = 7.4195e7 7.42e7 J

If the total mass of the car is 1070 kg, find the ratio of the initial rotational kinetic energy of the flywheel to the translational kinetic energy of the car.

0.5 I w^2/0.5 Mv^2 = 7.4195e7/(0.5*1070*20.6*20.6) = 326.8 327

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