Is it possible to measure the depth of a well using kinematic equations?

Explanation

Consider a well without water, of some depth d. Take a small object (for example lemon) and a stopwatch. When you drop the lemon, start the stop watch. As soon as the lemon touches the bottom of the well, stop the watch. Note the time taken by the lemon to reach the bottom and denote the time as t.
Since the initial velocity of lemon u=0 and the acceleration due to gravity g is constant over the well, we can use the equations of motion for constant acceleration.
`s=ut+(1)/(2)at^(2)`
Since u=0, s=d, a=g (Since choose the yaxis downwards), Then
`d=(1)/(2)"gt"^(2)`
Substituting `g=9.8ms^(-2)` we get the depth of the well.
To estimate the error in our calculation we can use another method to measure the depth of the well. Take a long rope and hang the rope inside the well till it touches the bottom Measure the length of the rope which is the correct depth of the well `(d_("correct"))`. Then
error = `d_("correct")-d`
relative error `(d_("correct")-d)/(d_("correct"))`
percentage of relative error `(d_("correct")-d)/(d_("correct"))xx100`
What would be the reason for an error, if any? Repeat the experiment for different masses and compare the result with `d_("correct")` every time.