Two equal masses are attached to the two ends of a spring of spring constant k. The masses are pulled out symmetricaly tostretch the spring by a length x over its natural length. The work doen by the spring oneach mass is

Explanation

(i) `+ 1/2 kx^(2)`
(ii) `-1/2 kx^(2)`
(iii) `+ 1/4 kx^(2)`
(iv) `-1/4 kx^(2)`