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Homework Help: Need help finding what formula to use?

  1. Sep 8, 2009 #1
    1. The problem statement, all variables and given/known data
    A tennis player hits a ball at ground level, giving it an initial velocity of 26 m/s^2 at 54 degrees above the horizontal. How high above the ground does the ball go?

    2. Relevant equations

    3. The attempt at a solution
    I found out the horizontal velocity, which is 15.3 and the vertical velocity which is 21.0
  2. jcsd
  3. Sep 8, 2009 #2
    In projectile motion the highest point occurs right in the middle when the vertical speed is zero.
  4. Sep 8, 2009 #3
    Yeah, I understand that. What formula would I use to actually find the height though?
  5. Sep 8, 2009 #4
    [tex]v^2=v_o^2+2a\Delta y[/tex]
  6. Sep 8, 2009 #5
    So if at the highest point there is a vertical speed of zero, would I put zero in for v^2? 26 for initial velocity and -9.8 for acceleration?
  7. Sep 8, 2009 #6
  8. Sep 8, 2009 #7
    the answer is 22.6, but when i do that I get 34.49
  9. Sep 8, 2009 #8
    ohh... I think I needed to put in the vertical velocity which was 21.0 instead. Then that formula works.
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