You are climbing in the high sierra when you suddenly find yourself at the edge of a fog-shrouded cliff. to find the height of this cliff, you drop a rock from the top; 10.0 s later you hear the sound of the rock hitting the ground at the foot of the cliff.

The total time it takes the sound to reach our on top of the cliff (10.0 s) is actually sum of two times:
- the time it takes the rock to hit the ground starting from the top of the cliff, t1
- the time it takes the sound to reach the top of the cliff starting from the ground, t2
1) The rock moves by uniformly accelerated motion, with constant acceleration . Its law of motion is given by , where is the initial velocity of the rock, and h is the height of the cliff. The time t1 is the time at which the rock reaches the ground, so that y(t1)=0, and the equation becomes

2) The sound moves from the ground to the top of the cliff by uniform motion, with constant speed v=343 m/s. Therefore, the sound covers the distance h (the height of the cliff) in a time t2 given by

3) If we rewrite h in both equations, we can write:
(1)
4) We also know that the sum of t1 and t2 is equal to 10 seconds:

from which we find

if we substitute this into eq.(1), we get

Numerically:

Solving the equation, we find the solution (the other solution is negative, so it does not have physical meaning). As a consequence,

and the height of the cliff is given by

Magma  is composed of molten rock and is  stored  in the earth's crust. lava is  magma  that reaches the surface of our planet through a volcano vent.