A constant force $\mathrm{F}$ applied on a body of mass $5 \mathrm{~kg}$, changes its velocity from $2 \mathrm{~m} \mathrm{~s}^{-1}$ to $7 \mathrm{~m} \mathrm{~s}^{-1}$ in 10 second. If the direction of motion is unchanged, applied force $\mathrm{F}$ is
(a) $2.5 \mathrm{~N}$
(b) $5 \mathrm{~N}$
(c) $7.5 \mathrm{~N}$
(d) $10 \mathrm{~N}$