# Problem 4-21-Projectile - A

A football is placed on a line $25\; m$ from the goalpost. The placement kicker kicks the ball directly toward the goalpost, giving it a velocity of $21.0\; m/s$ at an angle of $47.0^\circ$ above the horizontal. The horizontal bar of the goalpost is $3.0\; m$ above the field. How far above or below the horizontal bar of the goalpost will the ball travel?

We must choose a coordinate system in which to solve the problem. Which is best?

A. Correct

A and B are best. A has the advantage of making distances above ground positive so we will use it.
As with all projectile problems we must solve the vertical and horizontal motions separately. Which statement is correct?

(A)   The vertical motion is accelerated and the horizontal motion is not.
(B)   The horizontal motion is accelerated and the vertical motion is not.
(C)   Both the vertical and horizontal motions are accelerated
(D)   The acceleration is zero for both the vertical and horizontal motion.