Question

Two particles $A$ and $B$ initially at rest move towards each other under a mutual force of attraction. At the instant when velocity of $A$ is $v$ and that of $B$ is $2v$, the velocity of centre of mass of the system

• A. $v$
• B. $2v$
• C. $3v$
• D. $zero$

Answer 1

The correct option is D $zero$

The velocity of the center of mass will be zero. The initial velocity of the particles were zero because both $A$ and $B$ were at rest so momentum will be zero. and it is given that there is no external force hence no change in momentum of center of mass and it will remain zero.

By the law of conservation of momentum, the momentum is zero, and mass is not zero, velocity must be zero

Hence, The option $D$ is the correct answer