So, it will gradually decay, keep on decaying. So, there will be general acceleration induced on the fluid. Now, what happen? Let us look at the force, what is the force? It is mass of the rigid body, mass into acceleration, but now as I accelerate the body, I am also accelerating part of fluid mass. So, my total force has become this plus some additional part. We do not know how much the additional part. Now, what is happening? I can assume the additional part, this additional part of the force to be some equivalent mass into the same acceleration. Remember, this is very important, it is an equivalent concept.