I think b but I’m not completely sure
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.
The kinetic energy decreases
Answer:
We know that the torque can be calculated as follows:
T = rpsinα
With r being the distance of the body from the center of the circumference he has as trajectory, p being the momentum of the body and sinα being the sine of the angle between the 2 vectors: r and p.
It's pretty obvious that T is directly proportional to the momentum, that can be written as p = m·v, with m being the mass of the object and v the velocity of the object.