In the figure shown, the heavy ball of mass 2m rests on the horizontal surface and the lighter ball of mass m is dropped from a height h > 2l. At the instant the string gets taut, the upward the velocity of the heavy ball will be

Velocity of light ball, when it is descended by height 2lv=2g2l=2glWhen string will taut then impulsive tension will be generated in the string.Let velocity all both masses become v' after string taut.J=2mv' ---- (1) J=m×2gl-mv' ---- (2)(1) = (2)From conservation of linear momentum.m2gl=2mv′+mv′2mgl=3mv′23gl=v′