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Homework Help: Help with physics problem please.

  1. Sep 15, 2009 #1
    Projectile Motion and Level Horizontal Range.

    1. The problem statement, all variables and given/known data
    The acceleration of gravity is 32ft/s ^2.
    If a pitch were thrown horizontally with a velocity of 96.9 mi/h, how far would the ball fall vertically by the time it reached home plate, 60ft away. Answer in units of ft.
    So speed is 142.12 ft/s.

    2. Relevant equations
    Vx = Vxo + Axt
    Y= Yo + VyoT + 1/2AyT^2 or Vy^2 = Vyo^2 + 2Ay(Y-Yo)

    For the second equation, don't know which one to use.

    3. The attempt at a solution
    I got the time it took to reach 60 feet by using the first equation. T= 4.441. I don't know where to go from there. I think I use this equation: Y= Yo + VyoT + 1/2AyT^2

    but I'm not sure. Any help would be appreciated greatly.

    Edit: actually t= .422 seconds.
    Last edited: Sep 15, 2009
  2. jcsd
  3. Sep 15, 2009 #2
  4. Sep 15, 2009 #3
    Last edited: Sep 15, 2009
  5. Sep 15, 2009 #4
    I'm not sure what you are asking. Sorry to be such a pain.
  6. Sep 15, 2009 #5
    Sorry, ok so you know how long it takes for the ball to get from release to home. It travels a distance in the -y direction in that time. Thats what your looking for.
  7. Sep 15, 2009 #6
    using this equation: Y= Yo + VyoT + 1/2AyT^2, I got 57.151. That definitely is not right or is it?
  8. Sep 15, 2009 #7
    probably not what are you using for Vy at t=0? and if y=0 at the pitchers release what direction is acceleration in the y direction?
  9. Sep 15, 2009 #8
    I cannot figure out this problem. Maybe I got the time wrong. I don't even know what I'm looking for. Can somebody please clarify some stuff for me. I just want to know how to do it.
  10. Sep 15, 2009 #9
    You mean Vyo, I used the original speed the ball was thrown, 142.12 feet/s. Is that wrong?
  11. Sep 15, 2009 #10
    yes that is wrong. That is the Vox, what is the Voy if the ball is thrown horizontally?
  12. Sep 15, 2009 #11
  13. Sep 15, 2009 #12
    yep, and then what is the acceleration of the ball?
  14. Sep 15, 2009 #13
    OMG I just got it. Voy is 0! So it is -y = 1/2 (32) (.422)^2. Which gives me 2.849. Which is right in the computer. Thank you for your help!
  15. Sep 15, 2009 #14
    no prob!
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