At the Same Instant That a 0

Multiple Choice

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) 0.25g
B) 0.50g
C) 0.75g
D) g
E) g/0.75