How can the depth of well is measured and also estimate the % of real

1.	How can the depth of well is measured and also estimate the % of real error .
Answer» SOLUTION :(i) 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. (ii) Since the INITIAL velocity of lemon `u = 0` and the ACCELERATION due to gravity g is constant over the well, by using use the equations of motion for constant acceleration. `s=ut+(1)/(2)at^(2)` (iii) `u=0, s=d, a=g` (Since we choose the y axis downwards), Then `d=(1)/(2)g t^(2)` (iv) Substituting`g = 9.8 ms^(-2)`the depth of the well is obtained . (v) To estimate the error in calculation another method is used to measure the depth of the well . (vi) 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)` percentage of relative error `=(d_("correct")-d)/(d_("correct"))xx100`

How can the depth of well is measured and also estimate the % of real error .