A well has a depth of 
from ground level to the surface of the water in the well, as shown in the figure.
not scale
A student wishes to find the depth of the well. The student plans to drop a stone down the well and record the time taken from releasing the stone to hearing the splash made by the stone as it enters the water.
Assume that air resistance is negligible and that the stone is released from rest. Calculate the time taken for the stone to fall from ground level to the surface of the water.
The time recorded by the student using a stop-watch is not equal to the time in (a). Suggest three possible reasons, other than the effect of air resistance, for this difference.
The student repeats the experiment three times and uses the results to calculate the depth of the well. The values are shown in the table.
The true depth of the well is 
. Explain why these results may be described as precise but not accurate.
