The position-time graph of a body of mass $2 kg$ is as shown in figure. What is the impulse on the body at $t=4s$?

At $t=4s$, the body has constant velocity $u=\frac{3}{4}m{s}^{-1}$

After $t=4s$, the body is at rest i.e. $\nu =0$

Impulse $=m\left(\nu -u\right)=2kg\left(0-\frac{3}{4}m{s}^{-1}\right)=-\frac{3}{2}kg m{s}^{-1}$