Final answer:
A softball thrown backwards from a moving pickup truck could appear to fall straight down to a roadside observer if the truck travels at a constant speed and the throw cancels the truck's speed.
Step-by-step explanation:
It is indeed possible for the ball to appear to fall straight down from the perspective of a person standing at the side of the road if a person in the back of a pickup truck throws it straight backwards. This condition can occur when the truck is moving at a constant speed. For the ball to fall straight down as seen from the side of the road, the person would have to throw the ball backward with a speed that is equal in magnitude, but opposite in direction, to the speed of the truck. This would cancel out the forward motion of the ball relative to the ground. To the person who threw the ball, the motion would appear to go straight up and then straight back down because from their frame of reference, they have already imparted the necessary backward motion to cancel the truck's forward speed.