2. If v = 0 at an instant, i.e. if a body is momentarily at rest, it does not mean that force or acceleration are necessarily zero at that instant. For example, when a ball thrown upward reaches its maximum height, v = 0 but the force continues to be its weight mg and the acceleration is not zero but g.
Answers & Comments
Yes, that is correct. The fact that an object is momentarily at rest (i.e., has zero velocity) does not necessarily imply that the net force or acceleration acting on it is zero at that instant.
In the example of a ball thrown upward, when the ball reaches its maximum height, it has zero velocity and is momentarily at rest. However, the force of gravity (which is equal to the ball's weight, mg) continues to act on the ball even at this instant. Therefore, the net force acting on the ball is not zero, and neither is the acceleration, which is equal to the acceleration due to gravity, g.
This can be explained by the fact that velocity is just one component of an object's motion, and it is the net force that determines the object's overall motion. Even if an object's velocity is zero at a given instant, it can still be subject to a net force that will cause it to accelerate or change direction.
In summary, the fact that an object is momentarily at rest (i.e., has zero velocity) does not imply that the net force or acceleration acting on it is zero at that instant