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Homework Help: Projectile Motion

  1. Sep 19, 2007 #1
    1. The problem statement, all variables and given/known data
    A ball is kicked with initial speed 20 m/s and initial angle 40 degrees up an incline of angle 15 degrees. Assume that the ball leaves the ground a the base of the incline at [tex]x_{0}[/tex]=0 and [tex]y_{0}[/tex]=0. How far up the incline does the ball initially land (not how far horizontally or vertically but how far along the incline)?


    2. Relevant equations
    Range: [tex]R=(v^{2}_{0}/g)sin2\Theta_{0}[/tex]
    y-[tex]y_{0}=(tan(\Theta_{0})(x-x_{0})-g(x-x_{0})^{2}/2(v_{0}cos\Theta_{0})^{2}[/tex]

    3. The attempt at a solution
    Well what I tried was subtracting 15 from 40 and came up with 25 plugged it into the Range formula and went from got 31.3m. I think I am missing the the 15 degree incline and was wandering if I just multiplied the range by cos(15)?

    I also thought that finding the slope of the 15 degree line then setting it equal to the trajectory formula I could find the point of intersection and do some trig from there. In order to do that I would have to find the slope of the line. I was wandering if [sin(15)/cos(15)]x would be the slope of the 15 degree incline?

    Not sure which method works the first one seems like it could work but I was wondering if gravity changes when the angles are subtracted and if multipling by cos(15) is needed to make up for the incline?
     
    Last edited: Sep 19, 2007
  2. jcsd
  3. Sep 19, 2007 #2

    learningphysics

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    Homework Helper

    I recommend working the problem with the x-axis along the direction of the incline... the y-axis perpendicular to the incline... ie what is vx initial... what is vy initial... what is the acceleration in the x direction... what is the accleration in the y direction.

    then it is just a straight projectile problem.
     
  4. Sep 19, 2007 #3
    Ok that makes total sense thanks
     
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