Q. 37
The bob A of a pendulum released from horizontal to the vertical hits another bob B of the same mass at rest on a table as shown in Fig. 6.13. If the length of the pendulum is 1m, calculate
(a) the height to which bob A will rise after collision.
(b) the speed with which bob B starts moving. Neglect the size of the bobs and assume the collision to be elastic.

Answer :
Let be the mass of the bob and
be the initial height of the bob.
Potential energy of a particle raised to the height h is =
And kinetic energy of the particle with velocity v is given as
=
Just before collision, bob A reaches ground and its potential energy gets converted to kinetic energy,
∴ conserving energy we get,
-----(1)
(a) Using the result that when two bodies of same mass collide, their velocities are mutually interchanged,
Bob A must come to rest and bob B must gain the velocity in equation (1).
a) ∴ from above we conclude the bob A will not rise to any height since its velocity will become zero after collision.
b) ∵ the velocities are interchanged,
∴ velocity of bob B =
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During inelastic collision between two bodies, which of the following quantities always remain conserved?
Physics - Exemplar