# Dropping stone in mine shaft

1. May 17, 2007

### linhy

1. The problem statement, all variables and given/known data
one last problem..
IF you dropped a stone into a mine shaft that is 240 m deep. HOw soon after you drop the stone do you hear it hit the bottom of the shaft? Assume that temperature for this situation is 23.5 celcius

2. Relevant equations

So.. in order to get the wave speed i plug in
V= 331 m/s +(.6(23.5 C))
V= 345.1 m/s

I know that T is equal to the inverse of the frequency.. however i don't know how to get the frequency. Does anyone have a clue?

3. The attempt at a solution

2. May 17, 2007

### hage567

You don't need the frequency for this. You know the speed of sound, and the distance it travels. From that, you can work out the time it took for the sound to get back up the shaft.

You must also consider the time it took the stone to drop to the bottom of the shaft. That is important in your answer.

3. May 17, 2007

### linhy

so i have D= (1/2)gt^2... i solved for t and i got 6.93 second it took for the stone to get up. Then I used V = D/T .. so T = D/V.. hence.. afterward i got .695.. so i add the two answers i got together ...and got 7.623s. Does this answer sound resonable?

4. May 17, 2007

### hage567

It looks OK to me.

5. May 17, 2007

### linhy

well.. it looks reasonable to me too? thx! ^_^