Change in momentum(Δp)=Δ(mv)
mass will only change when the speed of this particular mass is near the speed of light So,
for c being very very large than the v
Δp=mΔv or m(v-u)
Now the rate of change of momentum Δp/t=m(v-u)/t
Δp/t=m×a As acceleration(a)=(v-u)/t
Δp/t=Force(F) As force=m×a
Hence ,The rate of change of momentum is equal to the force applied.
The rate of change of momentum is directly proportional to the force applied to body.