Work Power and Energy 4 Question 6

8. 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 l1/l2 is

(2013 Adv.)

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Answer:

Correct Answer: 8. 5

Solution:

  1. Velocity of first bob at highest point.

v1=gR=gl1

(to just complete the vertical circle)

=velocity of second bob just after elastic collision.

= velocity of second bob at the bottommost point =5gl2

l1l2=5



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