(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

If we include a crude model for the drag force in which the net acceleration on the ball kicked by a football player is given by:

a = (-k*v_{x})i+ (-g-k*v_{y})j.

Derive the equations describing the horizontal and vertical positions as functions of time.

k=.031 (1/s), v_{o}=69 (ft/s), [tex]\Theta[/tex]_{0}=45.

2. Relevant equations

3. The attempt at a solution

I solved for v_{x}and v_{y}using the information given (v_{x}=v_{0}cos[tex]\Theta[/tex], v_{y}=v_{0}sin[tex]\Theta[/tex] ) plugged these values, along with k, into the acceleration equation. I took the integral of both the horizontal and vertical components independently to get velocity, then integrated that to get the position. The problem is, the horizontal velocity comes out to be -1.51*t, and horizontal position is -.755*t^2, which is obviously wrong because it would be moving backwards the instant it is kicked. What am I doing wrong here? Should I not be solving for v_{x}and v_{y}, and leaving those as variables as well?

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# Homework Help: Projectile Motion question

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