Final answer:
A softball can fall straight down as viewed by a stationary observer if thrown backward with a velocity equal to the truck's forward velocity. For the thrower, the ball would seem to move backward before falling due to their shared momentum with the truck.
Step-by-step explanation:
It is indeed possible for a softball to fall straight down as viewed by a person standing at the side of the road if certain conditions are met. This could occur if the person in the back of the pickup truck throws the ball straight backward with a velocity exactly equal to the forward velocity of the truck. In this case, the backward velocity of the ball would negate the forward velocity imparted by the moving truck, resulting in the ball appearing to fall straight down to a stationary observer.
For the person who threw the ball, the motion would appear differently because they share the forward motion of the truck. To them, the ball would seem to move backwards at the same speed the truck is moving forward before falling to the ground, illustrating Newton's first law of motion that an object in motion tends to stay in motion, unless acted upon by an unbalanced force.