Projectile Motion

Question

(Ignore air resistance) A man is riding in the back of a truck (facing forward) that is driving forward at a constant velocity of 30 mph. If he throws a ball straight upward so that it reachers a maximum height of 40 ft above the road surface, the ball will land:

a) in front of the man

b) behind the man

c) in his arms

d) impossible to tell

Answer 1

The answer is C

The only force acting on the ball is gravity, which acts only in the vertical direction. When the ball leaves the man's hands, it is moving horizontally at 30 mph, and it retains that velocity throughout the whole trajectory because nothing is slowing it down in the horizontal direction

Note that we're ignoring air resistance - if air were present, then the ball would land behind the man, because the air would slow it down.

Answer 2

This is the same as if you are sitting in an airplane traveling 500 mph and you flip a quarter straight up in the air. The coin lands directly back down in your hand - it does not fly through the plane like a bullet at 500 mph. It continues in its horizontal motion - 500 mph relative to the ground, but stationary relative to the airplane, and to you.