Here, x(t)=pt+qt2+rt3
Where p=3ms−1,q=4ms−2,r=5ms−3 and m=2 kg
Velocity, v=dxdt=ddt(pt+qt2+rt3)=p+2qt+3rt2
Acceleration, a=dvdt=2q+6rt
At t=2s,a=2(4ms−2)+6(5ms−2)(2s)
=8ms−2+60ms−2=68ms−2
The force acting on the body of mass 2 kg is
F=ma=(2kg)(68ms−2)=136N