Question

Marcus dropped a penny into a wishing well and heard it hit the bottom exactly 1.5 seconds later. How deep is the well?

Answer 1

`~~11m`

Explanation:

We use the falling objects equation here, which is

`d=1/2g\t^2`

`g` is the gravitational acceleration `(9.81 \ "m/s"^2)`

`t` is the time in seconds

Plugging in the given values, we get

`d=1/2*9.81 \ "m/s"^2*(1.5 \ "s")^2`

`d=1/2*9.81 \ "m/s"^2*2.25 \ "s"^2`

`d=1/2*9.81 \ "m/"cancel("s"^2)*2.25cancel("s"^2)`

`d~~11.03 \ "m"~~11 \ "m"`

So, the well is approximately `11` metres deep.

Source (the equation):

https://en.wikipedia.org/wiki/Equations_for_a_falling_body