A dise of mass 
and radius 
is free to rotate in horizontal plane about a vertical smooth fixed axis passing through its centre. There is a smooth groove along the diameter of the disc and two small balls of mass 
each are placed in it on either side of the centre of the disc as shown in figure. The dise is given initial angular velocity 
and released. The net work done by forces exerted by disc on one of the balls (for the duration ball remains on the disc) is
Text Solution
Verified by ExpertsD
The angular speed of the disc when the balls reach the ends be 
. From the law of conservation of angular momentum
or 
The angular speed of the disc just after the balls leave the disc is 
Let the speed of each ball just after they leave the disc be 
.
From principle of conservation of energy
By solving we get, 
Work done by all forces is equal to change in K.E.,
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