NEET | 2017Rotational MotionHard

Question

Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities ω1 and ω2. They are brought into contact face to face coinciding the axis of rotation. The expression for loss of energy during this process is:-

Options

A.

14I(ω1-ω2)2

B.

I(ω1-ω2)2

C.

I8(ω1-ω2)2

D.

12(ω1+ω2)2

Solution

COAM :  Iω1+Iω2=2Iω ⇒ω=ω1+ω22
(K.E.)i = 12Iω12+12Iω22
(K.E.)f =12×2Iω2=Iω1+ω222
Loss in K.E. = (K.E.)i - (K.E)f = I4(ω1-ω2)2

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