Rotational dynamics about a fixed axis: The two rotating systems shown in the figure differ only in that the two identical movable masses are positioned at different distances from the axis of rotation. If you release the hanging blocks simultaneously from rest, and if the ropes do not slip, which block lands first?
A) The block at the left lands first.
B) The block at the right lands first.
C) Both blocks land at the same time.

Question

Rotational dynamics about a fixed axis: The two rotating systems shown in the figure differ only in that the two identical movable masses are positioned at different distances from the axis of rotation. If you release the hanging blocks simultaneously from rest, and if the ropes do not slip, which block lands first? 
A) The block at the left lands first. 
B) The block at the right lands first. 
C) Both blocks land at the same time.

Quizplus · Accepted Answer

The block on the right lands first. This is because it is closer to the axis of rotation, meaning it has a smaller radius and therefore a smaller moment of inertia. According to the law of conservation of energy, the total energy of the system is conserved. Therefore, the potential energy of the blocks is converted to kinetic energy as they fall. The block with the smaller moment of inertia can accelerate faster and therefore reaches the ground first.

Rotational Dynamics About a Fixed Axis: the Two Rotating Systems