Discussion Forum

A bob of mass m,  suspended by a string of length l₁,  is given a minimum velocity required to complete a full circle in the vertical plane, At the highest point, it collides elastically with another bob of mass m  suspended by a string of length l₂, which is initially at rest, Both the strings are massless and inextensible. If the second bob. After collision acquires the minimum  speed  required  to  complete  a full circle in the vertical  plane, the ratio  $\frac{l_{1}}{l_{2}}$  is 

Answer:

Explanation:

 Velocity of first bob at highesr point 

     $v_{1}=\sqrt{gR}=\sqrt{gl_{1}}$

  (to just completeb the vertical circle )

 = ve;ocity of second bob just after elastic collision,

  = velocity of second bob at the bottommost point     

=$\sqrt{5gl_{2}}$    $\therefore$    $\frac{l_{1}}{l_{2}}=5$