A string of length L and force constant k is stretched to obtain extension l. It is further stretched to obtain extension `l_(1)`. The work done in second streching is

A string of length L and force constant k is stretched to obtain extension l. It is further stretched to obtain extension l_(1) . The work done in second stretching is

An elastic string of unstretched length L and force constant k is stretched by a small length x. It is further stretched by another small length y. The work done in second stretching is

An elastic spring of unstretched length L and force constant K is stretched by amoun t x .It is further stretched by another length y The work done in the second streaching is