Ball A is dropped from rest from a window. At the same instant, ball B is thrown

Question

Ball A is dropped from rest from a window. At the same instant, ball B is thrown downward; and ball C is thrown upward from same window. Which statement concerning the ball after their release is necessarily true if air resistance is neglected? Why?

A. all three balls have the same velocity at any instant
B. All three balls have the same acceleration at any instant
C. All three balls strike the ground at the same time.
D. All three balls reach the ground with the same velocity
E. At some instant after it is thrown, the acceleration of ball C is zero.

Explanation / Answer

A is not true because they all have different velocities throughout their flight B is true, the only acceleration is due to gravity so they all have -9.8m/s^2 acceleration throughout their flights (only problem here is that C hits the ground before the others so its velocity changes while the other twos are still -9.8m/s^2) C is False, C hits first then A then B due to their initially velocities D is False, Using Newton's equations we see that they will all have different velocities when they hit the ground because of the difference in initial velocity. E is False/True False if you only look at its flight. True because it will hit the ground and come to a rest with zero net acceleration. All answers are based on a level of general physics.

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