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Homework Help: Finding the initial speed

  1. Oct 4, 2011 #1
    1. The problem statement, all variables and given/known data

    A baseball player throws a ball a distance of 250 ft. If the ball is released at an angle of 45°with the horizontal, find its initial speed.

    2. Relevant equations

    3. The attempt at a solution
    I don't know where to begin. All i know is that speed is the norm of velocity. Help?
  2. jcsd
  3. Oct 4, 2011 #2


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    Suppose the initial speed is v0. What are the vertical & horizontal components of the velocity.
  4. Oct 4, 2011 #3
    x=(v0cos 45°)t
    y=(v0sin 45°)t
  5. Oct 4, 2011 #4
    close. You forgot that the y equation has acceleration due to gravity, so that's [itex]\frac{-9.8}{2}[/itex][itex]t^{2}[/itex].

    And is that how I'm supposed to do math equations here? Cuz im relatively new (I signed up earlier, I just never used it till now).
  6. Oct 4, 2011 #5
    Yeah, that's how you do it. :smile: And thank you. I should use (32/2)t2 since the unit is feet. Correct?
  7. Oct 4, 2011 #6
    oh yeah, sorry but that, but glad I could help. :smile:
  8. Oct 4, 2011 #7
    So what do i do next? Differentiate?
  9. Oct 4, 2011 #8
    oh i thought you got it. Sorry. You know that x displacement is 250 ft, and y displacement is 0. If you plug that in, you'll find you have a system of two equations with two variables--initial velocity and time. I'm sure you can solve from there. :wink:
  10. Oct 4, 2011 #9
    Thank you so much! :smile:
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