1.

Using expressisions for power and kinetic energy of rotational motion, derive the relation `tau = I alpha`, where letters have their usual meaning.

Answer» We know that power in rotational motion,
`P = tau omega` ..(i)
and `K.E.` of rotation, `E = (1)/(2)I omega^(2)` …(ii)
As power=time rate of doing work in rotational motion, and work is stored in the body in the from of `K.E.`
`:. P = (d)/(dt) (K.E.` of rotation)
`= (d)/(dt) ((1)/(2)I omega^(2)) = (1)/(2)I xx 2 omega((d omega)/(dt))`
Using (i), `P = tau omega alpha` or `tau = I alpha`, which is the required relation.


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