As shown below, bob $A$ of a pendulum having massless string of length ' $R$ ' is released from $60^

Question

As shown below, bob $A$ of a pendulum having massless string of length ' $R$ ' is released from $60^{\circ}$ to the vertical. It hits another bob $B$ of half the mass that is at rest on a friction less table in the center. Assuming elastic collision, the magnitude of the velocity of bob $A$ after the collision will be (take $g$ as acceleration due to gravity).\

Professor PC Thomas Classes · Answer

(b) : From the diagram,\ $h=R-R \cos 60^{\circ}=R / 2$\ Applying conservation of energy,\ $m_{A} g h=\frac{1}{2} m_{A} v^{2} \Rightarrow m g\left(\frac{R}{2}ight)=\frac{1}{2} m v^{2}$