A rock is thrown upward with a velocity of 19 meters per second from the top of a 21 meter high cliff and it misses the cliff on the way back down. When will the rock be 11 meters from the water below?

Answer 1

the height h at time t is

h(t) = 21 + 19t - 4.9t^2
so, plug in h=11 and solve for t:

11 = 21 + 19t - 4.9t^2
t ~= 4.35 sec

Answer 2

5.93