A curious physics student drops a rock from a cliff that is 5.0 m above a pond. The rock hits the water with velocity v and then sinks to the bottom with the constant velocity v. It reaches the bottom of the pond 5.0 s after it is dropped. Find the depth of the lake
a. 10 m
b. 20 m
c. 30 m
d. 40 m
e. 50 m