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QuantumCurt

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## Homework Statement

A football punter kicks the football at a 30.0 degree angle above the horizontal and just scores a field goal 40.0 meters away, where the horizontal bar is 3.50 meters above the ground.

a. How long is the ball in the air before the goal is scored?

b. What was the initial speed of the ball right after the kick?

This is for college physics. We're doing two dimensional motion/kinematics right now. We just did projectile motion and vectors yesterday.

## The Attempt at a Solution

My first attempt was to put it in a vector form, using the x movement of 40.0m on the x-axis and 3.50 m on the y axis, giving me a vector of (40.0i+3.50j). And I couldn't see where to go from there.

I tried using the kinematic equation for motion in the y direction-

[tex]\Delta{x}=v_{0y}t+\frac{1}{2}gt^2[/tex]

[tex]3.50m=40.0m(\sin30)t+\frac{1}{2}(-9.80)t^2[/tex]

[tex]4.9t^2-20t+3.50=0[/tex]

Then I solved the quadratic and I got two solutions of 3.89 seconds, and .183 seconds. The 3.89 seems like reasonable length of time.

Am I on the right track here, or am I way off?

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