A small body A is fixed to the inner side of a thin rigid hoop of radius R and mass equal to that of the body A. The hoop rolls without slipping over a horizontal plane. At the moments when the body A gets into the lower position, the centre of the hoop moves with velocity
. The maximum value of
at which the hoop moves without bouncing is
. What is the value of
?
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The tendency of jumping of hoop will be maximum when the body A is at top most position.
Let at this position the linear velocity of hoop is V . So, velocity of the body is 2 V .
Now for hoop to jump, Centrifugal force given by the body on hoop must be greater than weight of the combined system.
So, F c p = R m V 2 = 2 m g (Here in F c p only V is taken into account and not 2 V because the velocity of body A relative to the centre of mass of hoop is V )
or, V = 2 g R
Since there is no energy loss, so we can use conservation of energy.
So, 2 1 I c m w i 2 + 2 1 ( 2 m ) v c m i 2 = ( 2 m ) g R + 2 1 I c m w f 2 + 2 1 ( 2 m ) v c m f 2
Therefore 2 1 2 R 2 3 m R 2 V o 2 + 4 m V o 2 = 2 m g R + 2 1 2 R 2 3 m R 2 V 2 + m ( 2 3 V ) 2 [Here v c m i = 2 V o & v c m f = 2 3 V ]
or, m V o 2 = 2 m g R + 3 m V 2
or, V o 2 = 2 g R + 3 V 2
Now putting the value of V = 2 g R in above equation
V o 2 = 2 g R + 3 ( 2 g R )
or, V o 2 = 8 g R
or, V o = 8 g R .
So to prevent hoop from jumping V o must be less than or equal to 8 g R .