# Homework Help: How deep is the well?

1. Jan 10, 2005

### ramollari

A stone is thrown into a well and the sound is heard after 3s. How deep is the well?

2. Jan 10, 2005

### dextercioby

Write down the times the stone takes to hit the water and the sound takes to reach your ear.You'll find your answer in no time...

Daniel.

3. Jan 10, 2005

You may also want to factor in the acceleration of the stone due to gravity.

4. Jan 10, 2005

### DaveC426913

Dex, you silly!

This is an assignment about acceleration, not about the speed of sound!

5. Jan 10, 2005

### dextercioby

Coul you explain both of your sentences???

Daniel.

6. Jan 10, 2005

### Pyrrhus

Use 343 m/s for the speed of sound, and remember the time given has the time when the rock falls and then the sound wave gets to you. Also the sound will be moving with constant speed.

7. Jan 12, 2005

### DaveC426913

I believe you missed the forest for the trees.

Your response seems to focus on the amount of time it takes the sound to reach your ear from the bottom of the well.

I believe the question is not about the speed of sound, it is about acceleration under gravity. The only relevant time delay concerns how fast the rock falls due to gravity. One should assume the delay due to propogation of sound is not a factor.

Maybe. I could be wrong.

8. Jan 12, 2005

### dextercioby

Dave,i believe you need a pair of glasses... :tongue2: My answer focuses on solving the problem:
,not on the speed of sound.It never mentions the speed of sound...

Since the solver needs to find the depth,a priori unknown,he must include the time of sound propagation,because he has no idea whether it can,or not be neglected.

Daniel.

9. Jan 12, 2005

### Curious3141

Doing it the "proper" way involves solving a quadratic. Assuming the speed of sound to be 340 m/s, there is an 8.5 % difference from the "easy" answer found by substitution.

I'm with Dexter on this one.

10. Jan 12, 2005

### DaveC426913

You don't think the grade K-12 homework problem is more simply stated as:

"How far will an object fall in 3 seconds"

?

11. Jan 12, 2005

### dextercioby

Don't u think that in the first 18 years of life one should know how to solve a quadratic equation??

Daniel.

12. Jan 12, 2005

### telko

edit: nvm nvm nvm

13. Jan 12, 2005

### UrbanXrisis

d=.5at^2
d=.5(9.8)(3s)^2
d=44.1m

time*acceleration = velocity
time*velocity = distance

14. Jan 13, 2005

### Zaimeen

ramollari did it say anything about the speed of sound in this question?