Question

prove that " mass is not constant"

Answer 1

Mass is not constant. If a body has its velocity approximate to the velocity of light in vacuum space, then by the theory of Relativity, mass of the body will change.

Answer 2

It can be proved simply using concepts of Classical Physics

We all know that P(momentum)=Mass×Velocity

Differentiating on both sides with respect to time, we get:

dP/dt=dM/dt ×dV/dt
dP/dt= (dM/dt× V) + (dV/dt ×M)

So....either mass can change with respect to time or velocity can change with respect to time...

When velocity changes with respect to to time, then the equation becomes
dP/dt=dV/dt ×M where M is constant(case-1)

When mass changes with respect to to time, then the equation becomes
dP/dt=dM/dt ×V where V is constant(case-2)


Eg of case 1: A ball hitting a wall
Eg of case 2: Propulsion of a rocket where mass of rocket changes with respect to time(since fuel gets consumed, the weight of rocket decreases)