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Projectile Motion diving board

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data

    You jump off a diving board with a horizontal velocity of 1.81 and land in the water 1.4 seconds later. Gravity=9.8. How high is this platform?

    2. Relevant equations
    x=2.534, if that helps.


    3. The attempt at a solution
    I got 7.07 but this is not right...
     
  2. jcsd
  3. Oct 20, 2009 #2

    rl.bhat

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    Hi Londoncalling, welcome to PF.
    What is the velocity in the vertical direction? What is the kinematic equation, which relates the initial velocity, time , acceleration and displacement?
     
  4. Oct 20, 2009 #3
    y=vit-.5gt2 right?
    I'm not sure though, we haven't learned it yet.
     
  5. Oct 20, 2009 #4

    rl.bhat

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    In the vertical direction the initial velocity is ....?
    Your equation is right. But put -y for the displacement because it is also in the downward direction like g.
     
  6. Oct 20, 2009 #5
    Okay so -y=vi -.5*9.8*1.42.
    Then -y=vi*1.4-(4.9*1.96)
    -y=vi*1.4-(9.604)
    But there are 2 variables and only one equation.... I thought you couldn't do that...?
     
  7. Oct 20, 2009 #6
    Or is your horizontal v of 1.81 the initial velocity?
     
  8. Oct 20, 2009 #7

    rl.bhat

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    The vertical velocity is zero.
     
  9. Oct 20, 2009 #8
    So it's 9.604 m high then?
    Edit: Yes, I got it right! Thank you SO much, you have no idea how relieved I am. Would you be able to help me with another problem (it's in a different post)....?
     
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