Two unequal masses M and m (M m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

Question

Two unequal masses M and m (M > m) are connected by a light cord passing over a pulley of negligible mass, as shown in the figure. When released, the system accelerates. Friction is negligible. Which figure below gives the correct free-body force diagrams for the two masses in the moving system?

Quizplus · Accepted Answer

For mass M, the only force acting on it is the tension in the rope pulling upward. For mass m, the force of gravity is pulling down and the tension in the rope is pulling up. As the system moves, the tension remains constant throughout the rope, so the diagrams in choices A and D, which show different tensions on each side of the pulley, are incorrect. Choice B shows gravity pulling up on mass m, which is incorrect. Therefore, the correct force diagrams are shown in choice C.

Two Unequal Masses M and M (M > M) Are