K is the force constant of a spring. The work done is increasing its extension from l_(1), to l_(2), will be

K is the force constant of a spring. The work done is increasing its e

1.	K is the force constant of a spring. The work done is increasing its extension from l_(1), to l_(2), will be
Answer» `K(l_(2)-l_(1))` `(K)/(2)(l_(2)+l_(1))` `K(l_(2)^(2)-l_(1)^(2))` `(K)/(2)(l_(2)^(2)-l_(1)^(2))` ANSWER :D