The initial momentum of the body = mu
Final momentum of the body = mv
Change in the momentum of the body in (t) seconds
= mv – mu
= m (v – u)
Rate of change of momentum = m (v – u)/t
= m × a [since m (v – u)/t]
Therefore,
Rate of change of momentum = ma = mass × acceleration.
This relation holds when the mass of the body remains constant.