Question

# Is the kinetic energy of the descending mass really negligible campared with that of the rotating...

Is the kinetic energy of the descending mass really negligible campared with that of the rotating objects as claimed above mgh = (8h^2I)/(D^2t^2) + W_F ?
The ratio of the two kinetic enrgies is 1/2 (m v^2)/(1/2 I w^2). This may easily shown to be:

(1/2 m v^2)/(1/2 I w^2) = (m D^2)/(4 I )

by using v = (w D)/2 .

this seems like an experiment based question .........isn't it ???

I can tell you the concept here. If you have any doubt, let me know

what you need to do is just put the value of mass (m) , diameter (D) and moment of inertia of ring in following equation

(m D^2) / (4 I ) - just solve this equation by putting in the values.

you will most probably get a value with a magnitude of more than 1 which means that the kinetic energy of the descending mass is really negligible compared with that of the rotating objects.

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