Sam and Terry find a 21.0 m deep wishing well and decide to make a wish. Terry throws a penny down the well at 7.00 m/s and Sam throws a penny up in the air at the same speed. If they threw them at the same time, how much time would there be between splashes?

Answer 1

The depth of the well does not matter.
How long does it take the coin thrown upwards to come back down to the top of the well?
7.00 - 9.81t = 0
That is how long it takes to stop rising and start falling. Double that, and you have the time between splashes.