Centre of Mass 1 Question 12

12. A block of mass M has a circular cut with a frictionless surface as shown. The block rests on the horizontal frictionless surfaced of a fixed table. Initially the right edge of the block is at x=0, in a coordinate system fixed to the table. A point mass m is released from rest at the topmost point of the path as shown and it slides down. When the mass loses contact with the block, its position is x and the velocity is v. At that instant, which of the following option is/are correct?

(2017 Adv.)

(a) The velocity of the point mass m is v=2gR1+mM

(b) The x component of displacement of the centre of mass of the block M is mRM+m

(c) The position of the point mass is x=2mRM+m

(d) The velocity of the block M is V=mM2gR

True/False

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Answer:

Correct Answer: 12. (a)

Solution:

  1. Δxcm of the block and point mass system =0

m(x+R)+Mx=0

where, x is displacement of the block.

Solving this equation, we get

x=mRM+m

From conservation of momentum and mechanical energy of the combined system

0=mvMVmgR=12mv2+12MV2

Solving these two equations, we get

v=2gR1+mM



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