A body  is hanging from a rigid support by an inextensible string of length 'l'. It is struck inelastically by an identical body of mass m with horizontal velocity v=2gl, the tension in the string increases just after the striking by

Conservation of linear momentum of the system of bodies just before and after collision yields                mv0=(m+m)v⇒v=v02∴ The tension in the string T=(2m)v2l+(2m)g              T=2mv024l+2mg=m(2gl)2l+2mg=3mgInitially the tension =T0=mg⇒ Increase in tension =2 mg