Question

When the velocity of an object is zero at an instant, the acceleration need not be zero at that instant. This statement is false but I have a doubt that at the top most point in motion under gravity is 0 but acceleration is g downwards. Please clear my doubt.

Answer 1

In the false statement it is mentioned 'instant'. So, it becomes false. But in case of gravity when velocity v becomes zero at the highest point, there takes place retardation which is negative acceleration. Now, because of Earth's gravity it has to come back to the Earth so, it increases it's velocity from 0 to any positive integer. Acceleration is the change in velocity and it is zero when velocity is constant. So, in this case velocity is increasing so acceleration will also be there with the value of a positive integer and as it is a vector quantity, it will have direction also.
Thanks.