Answer to Question 6

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The key to this is the moment of inertia.  The moment of inertia of the solid disk flywheel (ignoring the flange in the middle) is given by:

I = 1/2 Mr2

The second flywheel can, to a first approximation, be considered as a cylinder of mean radius, r.  The assumptions are 

  • that the thin part of the wheel has a mass that is very much smaller that the thick ring part.

  • the flange can be ignored.

The moment of inertia is given by:

I = Mr2

Therefore the second flywheel will have a moment of inertia that is double that of the first.  Therefore it will store double the kinetic energy for any given angular velocity.