Tuesday
February 9, 2016

# Homework Help: college physics

Posted by patti on Monday, March 18, 2013 at 12:46pm.

If a girl drops a coin into a wishing well. After exactly 5 seconds she hears it splash into the water. How fast was the coin going after 1 second? After 2 seconds? How fast was the coin going when it hit the water? How far down is the water? Could you please help with the formulas and the answers for these questions?
• college physics - drwls, Monday, March 18, 2013 at 1:15pm

OK, here is how to do that:

How fast was the coin going after 1 second? V(1) = 1*t = 9.8 m/s

After 2 seconds? V(2) = 2*t = 19.6 m/s

How fast was the coin going when it hit the water? V(T) = 5*T
Let T be the time when it hit the water.

It will also take the sound of the splash 340*T to be heard. 340 m/s is the assumed speed of sound.

How far down is the water?

Let H be the depth of the water in the well.

sqrt(2H/g) + H/340 = 5
You will have to solve that graphically, by iteration or the quadratic formula
H = 108 meters

Time when it hit water:
T = sqrt(2H/g) = 4.69 s
V(4.69) = 46 m/s