At the same instant that a 0.50-kg ball is dropped from 25 m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth's surface with an initial speed of 15 m/s.They move along nearby lines and pass without colliding.At the end of 2.0 s the acceleration of the center of mass of the two-ball system is:
A)0.25 g
B)0.50 g
C)0.67 g
D)0.75 g
E)1.0 g

Question

Quizplus · Accepted Answer

The acceleration of the center of mass of the system is determined by the external forces acting on the system divided by the total mass of the system. Since the only external force acting on both balls is gravity, and gravity acts equally on all masses regardless of their size (acceleration due to gravity, g, is constant), the acceleration of the center of mass of the system is equal to g, regardless of the individual motions of the balls.

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