You drop a 30 g pebble down a well. you hear a splash 2.7 s later. ignoring air resistance, how deep is the well? assume  g  = 9.8 m/s2. a- 0.79 m b- 36 m c- 71 m d- 790 m

I will assume here that the well is sufficiently short so that the time the sound takes to come from the bottom of the well to our ear is negligible.

Since the pebble moves by uniformly accelerated motion, the distance it covers is given by

where 
is the gravitational acceleration
is the time the pebble takes to reach the bottom of the well

Therefore, the depth of the well is

and the correct answer is B.