A body, starting from rest, attains a velocity of ${\text{20 ms}}^{-\text{1}}$ .The time taken by the body in the displacement of 50 m is                              

$\text{s}=\text{ut}+{\text{1/2at}}^{\text{2}}$                           ${\text{v}}^{\text{2}}-{\text{u}}^{\text{2}}=\text{2as}$

$50=\frac{1}{2}4{\left(\text{t}\right)}^2$                             ${\text{20}}^2=2\left(\text{a}\right)\left(50\right)$

$\text{t}=5\sec$                                   $20\times 20=1\text{00a}$

                                                $\text{a}={\text{4m/s}}^{\text{2}}$