The length of a spring is l and its force constant is k. When a weight W is suspended from it, its length increases by x. If the spring is cut into two equal parts and put in parallel and the same weight W is suspended from them, then the extension will be
Spring is cut into two equal halves so spring constant of each part = 2k
These parts are in parallel so
Extension force (i.e. W) is same hence by using .