How high is the cliff if a dropped rock is heard hitting the ocean after 3 seconds?

[monkeyboy726]

rock is dropped from cliff. it is heard hitting the ocean 3.00s later, if speed of sound is 340m/s, how high is the cliff?

im so stuck

 

[Chronos]

try d= (at^2)/2
a = acceleration
t = time
d = distance
use the speed of sound in dry air at sea level to solve.

 

[iamhumble]

Hi -

This is how I would approach this problem...

Draw a sketch to represent the situation. As you can see, the rock is in free fall from y (the height of the clift to the ground) to the ground (y = 0). The soundt travels with uniform speed the distance y (upward). Let t1 be the time of the free fall and t2 the time of the sound traveling up. Then, the total time is t = t1 + t2 = ?. Then, use the free fall formula to get time t1 and then solve for the height of the clift.

Good luck