Show that the rate of change of momentum $=$ mass $\times$ acceleration.

(N/A) Let a force $F$ act on a body of mass $m$ for time $t$ and change its velocity from $u$ to $v$.
Initial momentum of the body $= mu$
Final momentum of the body $= mv$
Change in momentum of the body in time $t = mv - mu = m(v - u)$
The rate of change of momentum $= \frac{\text{Change in momentum}}{\text{Time}} = \frac{m(v - u)}{t}$
Since acceleration $a = \frac{v - u}{t}$, we substitute this into the equation.
Therefore, the rate of change of momentum $= m \times a = \text{mass} \times \text{acceleration}$.
According to Newton's second law of motion, this rate of change of momentum is equal to the applied force $F$.