# Projectile Motion-Football Clearing Crossbar

1. Oct 6, 2012

### donjgatlin

1. The problem statement, all variables and given/known data

A Place kicker must kick a football from a point 36.0 m from the goal. As a result of the kick, the ball must clear the crossbar, which is 3.05 m high. When kicked, the ball leaves the ground with a speed of 20.0m/s at an angle of 53° to the horizontal.

Given:
Vi=20.0m/s
θ=53°
Δy=3.05m (Height it must travel to clear)
Δx=36.0m (Distance it must travel to clear)
Δt=2.99s

2. Relevant equations
a.) By how much does the ball clear or fall short of clearing the crossbar?
b.)Does the ball approach the crossbar while still rising or while falling?

For this question, I have already solved for Δt. After solving for the time, the uncertainty comes in as what to do next. Should I divide the time in half and solve for only the time the ball is falling downward?

3. The attempt at a solution
Δt=Δx/Vicosθ=2.99s

2. Oct 6, 2012

### voko

Since you know the time, you should be able to determine both the height and the vertical velocity at the time, and, thus, answer the questions.