Center of MassHard

Question

Two particles A and B each of mass m are attached by a light inextensible string of length 2l. The whole system lies on a smooth horizontal table with B initially at a distance l from A. The particle at end B is projected across the table with speed u perpendicular to AB. Velocity of ball A just after the jerk is -

Options

A.
B.u√3
C.
D.

Solution


When the string becomes tight, both particles begin to move with velocity components v in the direction AB. Using  conservation of momentum in the direction AB
mu cos 30o = mv + mv
or v =
Hence the velocity of ball A just after the jerk is v =
Mathod II.
                    
∴   = 0, using conservation of linear momentum along the string.
        m u cos 30o = mv + mv
        2v = u. ⇒ v = u

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