Let be the acceleration of the masses. By Newton's second law, we have
• for the masses on the left,
where is the magnitude of tension in the pulley cord, and
• for the mass on the right,
Eliminate to get
Starting from rest and accelerating uniformly, the right-hand mass moves up 75 cm = 0.75 m and attains an upward velocity such that
When the 0.5m mass is released, the new net force equations change to
• for the mass on the right,
where and are still tension and acceleration, but not having the same magnitude as before the mass was removed; and
• for the mass on the left,
Eliminate .
Now, the right-hand mass has an initial upward velocity of , but we're now treating down as the positive direction. As it returns to its starting position, its speed at that point is such that