AL phy SHM pendulum 有少少問題

If the angle (theta) is too larger (e.g. larger than 10 degrees), I don't think it would oscillate in simple harmonic motion.

As such, the period of oscillation is a little bit longer than the one with angular amplitude (alpha). The two masses would then collide somewhere to the left of the central vertical line.

2010-03-06 16:03:57 補充：
Sorry....I have overlooked that the angle (theta) is smaller than 10 degrees. Under such situation, to a good approximation, the two bobs will still collide at a point below the point of suspension.

Yes, the balls A and B will colide at x=0.
In simple harmonic motion, the period of the motion is independent of the amplitude (provided that the angle is small)
Hence, the time needed for A and B to travel from max. displacement to their equilibrium position (x=0) is the same