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Q.

A spherical ball of radius R and mass m collides with a plank of mass M kept on a smooth horizontal surface. Just before impact, the centre of the ball has a velocity v0 vertically downward and angular velocity ω0 as shown in the figure. After the impact, the normal velocity is reversed with same magnitude and the ball stops rotating after the impact. The coefficient of friction between the ball and the plank is μ . 
Assume that the plank is large enough. The distance on the plank between first two impacts of the ball is 4v0Rω0βg(1+mM).  Find the value of  β

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Detailed Solution

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The forces during impact are as shown in figure
 Question Image
Let the horizontal velocities of the plank and the ball be v2 and v1 in opposite directions as shown in
Figure
Question Image 
From conservation of linear momentum
 mv1=Mv2.......(i)
Linear impulse of the ball in vertical direction = Charge in linear momentum in vertical direction
J=2mv0..........(ii) 
 [J=ndt=Δp]
Linear impulse on the ball in horizontal direction =change in linear momentum in horizontal
Direction
 Jf=mv1.........(iii)
Angular impulse on the ball about centre of mass = change in angular momentum about centre of
Mass
 JfR=Iω0=25mR2ωo.....(iv)
Solving Eqs (i), (ii), (iii) and (iv) get
 v1=25Rω0andv2=mM(25Rωo)
Now, actual path of the ball is projectile, whose time of flight will be
T=2vyg=2vog 
Relative velocity of ball with respect to plank in horizontal direction is
vr=v1+v2=25(1+mM)Rωo 
So, the desired distance is
 s=vrT=45.voRωog(1+mM)

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