A body of mass 500 g moves along $x$-axis such that it's velocity varies with displacement $x$ according to the relation $v = 10 \sqrt { x } \mathrm {~m} \mathrm {~s} ^ { - 1 }$ the force acting on the body is:\\
(1) 125 N\\
(2) 25 N\\
(3) 166 N\\
(4) 5 N