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Homework Help: Projectile Motion - need help

  1. Oct 4, 2005 #1
    Projectile Motion -- need urgent help :)

    If a projectile is fired from the origin of the coordinate system with an initial velocity v and in a direction making an angle alpha with the horizontal, calculate the time required for the projectile to cross a line passing thorugh the origin and making an angle beta less than alpha with the horizontal.

    I know that the position of the projectile is described by
    y=y0+v0(sin alpha)*t-4.9t^2.

    I let the line be y=ax. I also drew a triangle with Beta as the angle, y=ax as the opposite side, and x as the adjacent side. I'm assuming I want to find y in terms of Beta and then set this equal to y in my projectile motion equation...then solve for t???

    Thanks in advance!!!
  2. jcsd
  3. Oct 4, 2005 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Combine this with the equation for the horizontal position and you can get y as a function of x.

    Write the equation of the straight line. (What is "a" in terms of beta?)

    Now you can find the value of x where the two functions intersect. And then plug that into one of the other equations to solve for the time.
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