A body of mass $m$ starts moving from rest along $x$-axis so that its velocity varies as $v = a \sqrt { s }$ where $a$ is a constant and $s$ is the distance covered by the body. The total work done by all the forces acting on the body in the first $t$ second after the start of the motion is\\
(1) $8 m a ^ { 4 } t ^ { 2 }$\\
(2) $\frac { 1 } { 4 } m a ^ { 4 } t ^ { 2 }$\\
(3) $4 m a ^ { 4 } t ^ { 2 }$\\
(4) $\frac { 1 } { 8 } m a ^ { 4 } t ^ { 2 }$