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