oh...got it..thanx..
even i did silly wala mistake!!! [4]
Three identical balls are connected by light inextensible strings with each other as shown and rest over a smooth horizontal table. At the moment t=0, ball B is imparted a velocity. Calculate the velocity of A when it collides with C.

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5 Answers
lol..
i cahanged answer thrice.. did calculation msitake..
Now by conservation of momentum when A and C collides... velcoity of B=v_{0}/3
By conservation of energy
mv_{0}^{2}/2=1/2m(v_{0}/3)^{2}+2mx^{2}/2
x is speed of A and C
x= 2v_{0}/3
where V_{o}/3 is velocity in upward direction... so right componetn=v_{0}/√3
if not clear how velocity v_{0}/3
it is by conservation of momentum
finally when distance between A and C=0
then for the length to be L the velocities of all of them must be same
hence
mv_{0}=3mv^{'}
tanx for giving the explanation... mere ko aaram ho gaya.. [4] [1]