Rotation + Moment of Inertia

BITSAT 2015 Sample Questions › Mechanics questions › Rotation + Moment of Inertia

Suppose a mass 'm' sticks to a rotating disc of mass M and radius R.
I wanted to whether new I = (M+m)R²/2 or (MR²/2 + mR²)
If second is correct then please give me an example in which first one is used.

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2 Answers

kaymant ·2010-10-14 19:23:05

Assuming the mass m is a point mass and sticks at the periphery of M, the second one is true. On the other hand if the mass m is in form of a disc of the same radius R, then the first one can be used. The basic idea behind the results is the fact that moment of inertia is an additive quantity; you can add the moments of inertia about the same axis.