Question

A proton and an electron, initially at rest, are allowed to move under their mutal attractive force. Their centre of mass will:

• A. remain stationary
• B. move towards the electron
• C. move in an unpredictable manner
• D. move towards the proton

Answer 1

Answer: (A)

remain stationary

We require an external force to move the centre of mass of a system of particles. The mutual force of electrical attraction is an internal force which can not affect the position of the centre of mass of the system.