The distance travelled by an object in time $t$ is given by $s = 2.5 t ^ { 2 }$. The instantaneous speed of the object at $t = 5 \mathrm {~s}$ will be :\\
(1) $25 \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(2) $5 \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(3) $62.5 \mathrm {~m} \mathrm {~s} ^ { - 1 }$\\
(4) $12.5 \mathrm {~m} \mathrm {~s} ^ { - 1 }$