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Question

The moment of inertia of two rotating bodies are IA and IB (IA IB) and their angular momenta are equal. Which one has greater kinetic energy?

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Solution

L= angular momentum
I = moment of inertia
w = angular velocity
Suppose Ia > Ib
​We know that
L = Iw ( formula)
Given ​angular momenta are equal:
La = Lb
Ia wa = Ibwb
wa/wb = Ib/Ia ...................(1)
this means wb >wa
K.E (kinetic energy) = 1/2 * I * w2
KEa=​1/2 * Ia * wa2
KEb=1/2 * Ib * wb2

KEa/KEb= ​Ia * wa2 / ​Ib * wb2
from eq (1)
KEa/KEb= wa/wb ................(2)
so KE of b is graeter with Inetia as Ib

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