0Suppose an object having mass m has an initial velocity u and after certain time t it attains a velocity v.
Now momentum P1=mu and P2=mv
So change in momentum
=P2-P1=mv-mu
=m(v-u)
So the rate of change in momentum
=m(v-u)/t
Now momentum is proportional to the applied external force.
So,
F=m(v-u)/t
We know that acceleration=(v-u)/t
Therefore, F=m × a
In other word Force=mass×acceleration
