A body of mass 10   kg is moving with an initial speed of 20   m   s - 1 . The body stops…

Friction force wil act opposite to the motion of the body.

$F=\mu N=\mu mg$

$\Rightarrow a=-\mu g\left(\text{-ve sign for direction relative to the motion of body}\right)$

Now, applying equation of motion, we get

$v=u+at$

$\Rightarrow 0=20+\left(-\mu \times 10\right)\times 5$

$\Rightarrow 50\mu =20$

 $\Rightarrow \mu =0.4$