Refer to figure , where A and B represent the two extreme positions of a S.H.M. For velocity, the direction from A to B is taken to be positive. The acceleration and the force, along AP are taken as positive, and along BP are taken as negative.
(a) At the end A, the particle executing S.H.M.is momentarily at rest being its extreme position of motion. Therefore, its velocity is zero, acceleration is `+ve` because it is directed along AP. Force is also `+ve` since the force is directed alonog AP, i.e., `+ive` direction.
(b) At the end B, velocity is zero. Hee, acceleration and force are negative as they are directed along BP, i.e., along negative direction.
(c) At the mid point of AB going towards A, the particle is at its mean position P, with a tendency to move along PA, i.e., `-ve` direction. Hence velocity is `-ve`. Both, acceleration and force are zero.
(d) At 2 cm away from B going towards A, the particle is at Q, with a tendency to move along QP, which is negative direction. Therefore, velocity , acceleration and force, all are negative.
(e) At 3cm away from A going towards B, the particle is at R, with a tendency to move along RP, which is positive direction. Here, velocity, acceleration and force, all are positive.
(f) At 4 cm away from A going towards A, the particle is at S, with a tendency to move along SA,which is negative direction for velocity is negative but acceleration is directed towards mean positiion, i.e., along SP, hence `+ve`. Similarly, force is alos `+ve`.
