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Two particles which are initially at rest, move towards each other

Two particles which are initially at rest, move towards each other under the action of their internal attraction. If their speeds are v and 2v at any instant, then the speed of centre of mass of the system will be:

Options

(a) 2v
(b) zero
(c) 1.5
(d) v

Correct Answer:

zero

Explanation:

If no external force actson a system of particles, the centre of mass remains as rest. So, speed of centre of mass is zero.

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