Projectile Motion

Question

1) A rifle is shot horizontally at a speed of 200m/s above flat ground. Compared to a bullet that is dropped at the same instant, the bullet that is shot will:

a) take a longer time to reach the ground

b) take a shorter time to reach the ground

c) take the same amount of time to reach the ground

d) is it impossible to tell

2) 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

1) In the vertical direction there's only one force, Gravity, so acceleration is 9.8 m/s². So both accelerate down at the same rate, the horizontal moving bullet also has velocity in the horizontal direction, but that doesn't affect its velocity in the vertical direction. So C is the answer.

2) (ignore air resistance) The ball has a the same velocity as him while he's holding it, so when he throws it up it has a vertical velocity but that doesn't affect the fact that it still has the 30 mph horizontal velocity, so in the time it takes to go up 40 ft and down, it has the same horizontal velocity as the man so it moves the same amount as the man in that time, and it will land in his arms. So the answer is C.