Final answer:
At time t=0, when the ball is dropped from rest, its velocity is zero because it has not started moving yet.
Step-by-step explanation:
If ball 1 is dropped from rest at time t=0, the velocity of ball 1 at time t=0 is zero. This is because at the exact moment of release, the ball has not yet begun to fall, so it has no speed in the vertical direction. As time progresses and the ball begins to fall, affected by gravity, its velocity will start increasing in the downwards direction (negative velocity when considering downward as negative). However, at t=0, just as the ball is released and before it starts to accelerate due to gravity, its velocity is indeed zero.