Question
A vertical spring with force constant k is fixed on a table. A ball of mass m at a height h above the free upper end of the spring falls vertically in the spring. so that the spring is compressed by a distance d. The net work done in the process is:
Solution
B.
Work done is equal to change in energy of the body.
The situation is shown in the figure. When mass m falls vertically on spring, then spring si compressed by distance d.
Hence, network done in the process is
W= Potential energy stored in the spring + Loss of potential energy of mass 
