Question

The diagram shows two balls released from a device at the same time. The ball on the left falls freely from rest, and the ball on the right is launched horizontally. Which best compares the vertical motion of the two balls?
Both balls have constant velocity and are acted on by gravity.
Both balls are acted on by gravity and are accelerating downward.
Both balls are pulled downward and have zero acceleration.
Both balls have zero acceleration and have constant velocity.

Answer 1

As you can see, the gaps between balls are continuously rising. Which means, ball is acted upon by gravitational force. If it is acted upon by force, that means ball is under acceleration. Ball is under free fall, so it is falling down at            9.8 m/s/s. The ball which is projectiled and the ball which was dropped will have same velocity in downward direction. i.e, downward component of velocity for both the balls will remain same so they will reach ground at the same. Horizontal component of velocity of right ball won't affect its downward motion. 

Answer 2

Best answer is :
Both balls are acted on by gravity and are accelerating downward.

The acceleration of the balls is downward gravity... having an acceleration means the velocity is not constant.