A rock is dropped from a tree of height 20 m into a lake (depth 4.6 m) below. After entering the water, the rock floats gently down through the water at a constant speed of 1.6 m/s to the bottom of the lake. What is the total elapsed time?

Answer 1

h = 0.5g*t1^2 = 20 m.
4.9*t1^2 = 20
t1^2 = 4.08
t1 = 2.02 s.

d = r * t2 = 4.6 m.
1.6t2 = 4.6
t2 = 2.9 s.

T = t1 + t2 = 2.02 + 2.9 = 4.92 s.