When a ball is dropped into a lake from a height 4.9 m above the water level, it hits the water with a velocity v and then sinks to the bottom with the constant velocity v. It reaches the bottom of the lake 4.0 s after it is dropped. The approximate depth of the lake is :
(A) 19.6 m
(B) 29.4 m
(C) 39.2 m
(D) 73.5 m
