A student takes a photograph of a steel ball of radius 
as it falls from rest. The image of the ball is blurred, as illustrated in the figure below. The image is blurred because the ball is moving while the photograph is being taken.
The scale shows the distance fallen from rest by the ball. At time 
, the top of the ball is level with the zero mark on the scale. Air resistance is negligible.
Calculate, to an appropriate number of significant figures,
the time the ball falls before the photograph is taken,
the time interval during which the photograph is taken.
.
