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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
A
v
B
2v
C
Zero
D
1.5 v
Detailed Solution
The particles attract each other; these are internal forces of the system. There is no external force.
$\vec{F}_{ext} = M\vec{a}_{cm} = 0$, so the velocity of the centre of mass remains constant.
Initially both particles are at rest, so the velocity of the centre of mass is zero.
It therefore remains zero at every later instant, whatever the individual speeds (v and 2v) are.
Speed of the centre of mass = zero
$\vec{F}_{ext} = M\vec{a}_{cm} = 0$, so the velocity of the centre of mass remains constant.
Initially both particles are at rest, so the velocity of the centre of mass is zero.
It therefore remains zero at every later instant, whatever the individual speeds (v and 2v) are.
Speed of the centre of mass = zero