Refer figure, here A and B represent the two extreme positions of a simple harmonic motion. For velocity, the direction from A to B is taken to be positive. For acceleration and the force, the direction is taken positive if directed along AP and negative if directed along BP.
(a) At the end A, the particle executing simple harmonic motion 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 along AP, i.e., +ve direction.
∴ 0, + , +
(b) At the end B, velocity is zero. Here, acceleration and force are negative as they are directed along BP, i.e., along negative direction.
∴ 0, –, –
(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.
∴ –, 0, 0
(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. Here velocity, acceleration and force, all are negative.
∴ –, –, –
(e) At 3 cm 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 B going towards A, the particle is at S with a tendency to move along SP which is negative direction. Here, velocity, acceleration and force, all are negative
∴ –, –, –