Final answer:
A softball thrown from the back of a moving pickup truck can appear to fall straight down to an observer on the side of the road if it is thrown backward with a velocity equal to the truck's speed. From the thrower's perspective, the ball would appear to move straight backward.
Step-by-step explanation:
If someone is riding in the back of a pickup truck and throws a softball straight backward, it is possible for the ball to fall straight down as viewed by a person standing at the side of the road if the ball is thrown with a velocity exactly equal and opposite to the velocity of the truck. For this condition to occur, the throw must counteract the forward velocity the ball has due to the movement of the truck, resulting in a net velocity of zero in the horizontal direction relative to the ground.
To the person who threw the ball, the motion would appear as if the ball is moving straight backward with a velocity equal to the forward velocity of the truck. This is due to their perspective moving along with the truck, observing the ball's relative backward velocity.