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Homework Help: Completely stuck on projectile motion prob

  1. Oct 9, 2005 #1
    In a football game a kicker attempts a field goal. The ball remains in contact with the kicker's foot for 0.050 s, during which time it experiences an acceleration of 340 m/s2. The ball is launched at an angle of 47° above the ground. Determine the horizontal and vertical components of the launch velocity.

    **I tried using the equation:
    x=VoxT + 1/2axT^2 and setting the inital velocity of the X component to zero, but that didn't work. I am so stuck on how to do this problem in the slightest bit! Please help!
  2. jcsd
  3. Oct 9, 2005 #2
    why would you use this equation? x=VoxT + 1/2axT^2

    Use this one, V=v_0 + at

    assuming that the kicker hits the ball along 47 degrees during the entire length of contact.

    Then you can use sin and cos to break that down into horizontal and verticle components of launch velocity.
  4. Oct 9, 2005 #3
    I really don't understand what you mean by breaking it down into the y and x components by using sin and cos. What is my initial velocity that I will enter into that formula? And when I find that value, where do I go from there?
  5. Oct 9, 2005 #4
    Have you learned about momentum and impulse yet?

    If so this is a simple problem.

    The ball is initially at rest so it's initial momentum is zero. THe change in momentum is the impulse
    cancel the masses to get: a*dt=v

    Solve for v and then it's a simple matter of finding the components.
  6. Oct 9, 2005 #5
    No, sorry we haven't learned about momentum yet. This is only chapter 3 of the first physics..so this and kinetics are the only things we've covered.
  7. Oct 9, 2005 #6
    Thank you all for the help, I just figured out what you meant by using sin and cos to find the x and y velocities and it worked out. Thanks!!
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