5kg rock is dropped into a well and a splash is heard after 3 seconds , how deep is the well? Ignore air resistance

1 answer

you need to know the speed of sound (v). The total time is time to fall plus time to wait for the sound.

If the depth is s,

s = 1/2 gt^2 + v(3-t)
Plug in g and v and you get s.

The 5kg is spurious. Time to fall does not depend on mass.