Question

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

• A. zero
• B. v
• C. 2v
• D. 3v

Answer 1

Answer: (A)

zero

Answer 2

Initially both particles were at rest so ${{v}_{cm}}=0.$ As external force on the system is zero. Therefore velocity of centre of mass remain unaffected.