Question

One end of a light spring of spring constant k is fixed to a wall and the other end is tied to a block placed on a smooth horizontal surface. In a displacement, the work done by the spring is 12kx212kx2. The possible cases are
(a) at spring was initially compressed by a distance x and was finally in its natural length
(b) it was initially stretched by a distance x and and finally was in its natural length
(c) it was initially in its natural length and finally in a compressed position
(d) it was initially in its natural length and finally in a stretched position.

Answer 1

The possible cases are at spring was initially compressed by a distance x and was finally in its natural length  and it was initially stretched by a distance x and and finally was in its natural length.

Explanation:

Only (a) and (b), the work done will be positive.

Since in the conditions of (c) and (d) spring does not exert a force that is in the direction of displacement but in the opposite, so the work done will be negative.  

Answer 2

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