A parachutist drops first freely form an areophone for `10 s` and then his parachut opens out. Now he descends with a net retardtion of `2.5 ms^(-2)` If the balil out of the plane at a height of `2495 m` and `g=10 ms^(-2)`, his velocity on reaching the ground will be`.
A. `5 m s^(-1)`
B. `10 ms^(-1)`
C. `15 ms^-1)`
D. `20 ms^(-1)`