A loaded truck of mass 10 ton is going at a speed of 20 kmph. A box of mass 2 ton slips from it and falls on the road, then velocity of truck is

$\mathrm{M}=10\text{ ton }\mathrm{u}=20\mathrm{kmph}$

$\begin{array}{l}{\mathrm{m}}_1=8\text{ ton }\hspace{0.25em} \hspace{0.25em}\hspace{0.25em}\hspace{0.25em}{\mathrm{v}}_1=?\\ {\mathrm{m}}_2=2\text{ ton }\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em} {\mathrm{v}}_2=0\end{array}$

from 1^st law of conservation of linear motion

$\mathrm{MU}={\mathrm{m}}_1{\mathrm{v}}_1+{\mathrm{m}}_2{\mathrm{v}}_2$

$\begin{array}{r}10\left(20\right)=8\left({\mathrm{v}}_1\right)+2\left(0\right)\\ 200=8{\mathrm{v}}_1\\ {\mathrm{v}}_1=\frac{200}{8}=25\mathrm{kmph}\end{array}$