Question

How to find whether the system is at rest or accelerating

Answer 1

if external force is applied to a body the body is in rest.but if you applied an external force the body will accuire some motion hence, the body is in acceleration.

Explanation:

if you don't apply any external force the system or a body will stay at the same place as the time passage...but if you apply focre there will be change in the position of the body and hence,it accuire acceleration.