Two unequal masses hang from either end of a massless cord that passes over a frictionless pulley.Which of the following is true about the gravitational potential energy (U)and the kinetic energy of the system (K)after the masses are released from rest? A)$\Delta$U 0 B)$\Delta$U = 0 and $\Delta$K 0 C)$\Delta$U 0 and $\Delta$K

Question

Two unequal masses hang from either end of a massless cord that passes over a frictionless pulley.Which of the following is true about the gravitational potential energy (U)and the kinetic energy of the system (K)after the masses are released from rest? A)$\Delta$U < 0 and $\Delta$K > 0 B)$\Delta$U = 0 and $\Delta$K > 0 C)$\Delta$U < 0 and $\Delta$K = 0 D)$\Delta$U = 0 and $\Delta$K = 0 E)$\Delta$U > 0 and $\Delta$K < 0

Quizplus · Accepted Answer

When the masses are released, the heavier mass will accelerate downwards while the lighter mass will accelerate upwards. As a result, the gravitational potential energy of the system will decrease as the heavier mass moves down and the lighter mass moves up. This means that the change in gravitational potential energy, ΔU, is negative.
At the same time, the system will also gain kinetic energy as the masses move, since they are accelerating. This means that the change in kinetic energy, ΔK, is positive.
Therefore, the correct choice is A, where ΔU < 0 and ΔK > 0.

Two Unequal Masses Hang from Either End of a Massless Δ\DeltaΔ

Two Unequal Masses Hang from Either End of a Massless $\Delta$