1. The problem statement, all variables and given/known data Two particles are executing simple harmonic motion of the same amplitude A and frequency ω along the x-axis. Their mean position is separated by distance X0 (X0 > A). If the maximum separation between them is (X0 + A), the phase difference between their motion is My answer is π/2 but the answer given is π/3. 2. Relevant equations x = Asin(ωt + φ) 3. The attempt at a solution To me it looks like this: When the first particle is at it's mean position, the second particle is at it's extreme position, so that the distance between both of them is X0 + A. So, the phase difference should be π/2 In terms of coordinates, let mean pos of P1 be x=0, mean pos of P2 be X0. Let P1 go from x= -A to x = +A and P2 go from x = X0 - A to x = X0 + A. The situation here represents P1 at x=0 and P2 at x = X0 + A.