Calculating the Depth of a Well and Velocity of a Rock Using Equations of Motion

[Miri McPherson]

1. A rock is dropped into a well of an unknown depth. 20 seconds after the rock is dropped the splash is heard at the top of the well. What is the depth of the well? What is the velocity of the rock when it reached the bottom?2. X= Xo + Vo(t) + 0.5(a)(t^2)
V= Vo + a(t)
(V^2)= (Vo^2) + 2a(X-Xo)
Velocity of sound in air=343 m/s
Acceleration of gravity= -9.80 m/(s^2)

3. 0= Xo + 0.5(-9.80)(20-t of sound)
X= 343(t)
I feel like there isn't enough information, but I'm not sure. Any help would be greatly appreciated.

 

[Bystander]

Which time are you indicating with "t?" Fall time? Or, travel time of the splash noise? Or, total time?

 

[Miri McPherson]

Which time are you indicating with "t?" Fall time? Or, travel time of the splash noise? Or, total time?

The time is from the time that the rock was dropped until the sound was heard.

 

[berkeman]

The time is from the time that the rock was dropped until the sound was heard.

Welcome to the PF.

Divide it up into two times and two equations. Can you take a cut at doing that?