Problem 4-21-Projectile - Part 6 - B

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

Diagram of football being kicked and all forces acting on it.


Accumulated Solution

v0x=21cos47=(21)cos47=14.32m/sv0y=21sin47=(21)sin47=15.36m/sx=vxtt=x/vx=25m/14.32m/s=1.75s


y=v0t+(1/2)at2

Correct.

The acceleration of gravity in our coordinate system is:

(A)   positive

(B)   negative