A paratrooper jumps from a height $\mathrm{H}$. The parachute can provide a uniform deceleration of $2 \mathrm{~m} \mathrm{~s}^{-2}$. The height above the ground at which the parachute should be opened so that he touches ground with zero speed is $\left(\mathrm{g}=10 \mathrm{~m} \mathrm{~s}^{-2}\right)$
(a) $\frac{\mathrm{H}}{6}$
(b) $\frac{4 \mathrm{H}}{5}$
(c) $\frac{5 \mathrm{H}}{6}$
(d) $\frac{6 \mathrm{H}}{7}$