Free Fall Problem in Physics?

Question

Uhm could you please help me solve these problems. I was studying for my Physics exam and these were the 2 free fall problems that I couldn't answer. Please show me the solution so that I can study it. tnx!

1. A stone is thrown vertically upward with a speed of 12.0m/s from the edge of a cliff 70.0 m high.

a. how much later does it reach the bottom of the cliff?

b. What is its speed just before hitting?

c. What total distance did it travel?

2. A rock is dropped from a sea cliff, and the sound of its striking the ocean is heard 3.2s later. If the speed of sound is 340 m/s, how high is the cliff?

Answer 1

sturm is wrong on #2 unless of course, the rock falls faster than the speed of sound.

a rock will not hit the water in 3.2 seconds from a cliff over 1 Km high....

Answer 2

The time necessary to reach the highest position is:

t = -12.0 m/s / -9.80 m/s² = 1.22 s

The maximum height of the stone is:

h = 0 m + (12.0 m/s x 1.22 s) + (0.5 x -9.80 m/s² x (1.22 s)²) = 7.35 m

The final velocity is:

v = (2gh)^(1/2) = (2 x 9.80 m/s² x 77.3 m)^(1/2) = 38.9 m/s

The total time is:

1.22 s + (38.9 m/s / 9.80 m/s²) = 5.19 s

The total distance traveled is:

70.0 m + (7.35 m x 2) = 84.7 m