Objects X and Y are connected by a string of negligible mass and suspended vertically over a pulley of negligible mass, creating an Atwood's machine, as shown in the figure. The objects are initially at rest, and the mass of object Y is greater than the mass of object X. As object Y falls, how does the kinetic
energy of the center of mass of the two-object system change? Justify your selection. All frictional forces are considered to be negligible.
А
The kinetic energy increases because the gravitational force due to Earth does positive net work on the system.
B
The kinetic energy increases because the gravitational force due to Earth does negative net work on the system.
с
The kinetic energy decreases because the gravitational force due to Earth does positive net work on the system.
D
The kinetic energy decreases because the gravitational force due to Earth does negative net work on the system.