A hollow sphere is filled with water weighing as much as the sphere. It then does pure rolling.
The ratio of the of the system when the water is liquid to that when it is solid is of the form where and are co prime integers.
Find
The velocity of the system in both the cases is same.
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When water is liquid in the sphere it will have no rotational kinetic energy also m s p h e r e = m W a t e r , so we write kinetic energy of the system as :
K . E 1 = 2 1 m s p h e r e v 2 + 2 1 m w a t e r v 2 + 2 1 ( 3 2 m s p h e r e r 2 ω 2 ) = 3 4 m v 2
Note I am using the conditions of pure rolling that is v = ω r
When water is solid it will also have rotational kinetic energy. So now we write it's kinetic energy as :
K . E . 2 = 2 1 m s p h e r e v 2 + 2 1 m w a t e r v 2 + 2 1 ( 3 2 m s p h e r e ω 2 r 2 ) + 2 1 ( 5 2 m W a t e r ω 2 r 2 ) = 1 5 2 3 m v 2
Dividing these two we have :
K . E 2 K . E 1 = 2 3 2 0
Pratik you should mention in the question that we have to assume same velocity in both the cases.