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Homework Help: Projectile motion trampoline

  1. May 25, 2016 #1
    1. The problem statement, all variables and given/known data
    You jump straight upward off a trampoline with an initial velocity of 30 km/h. How high above the trampoline will you reach?

    2. Relevant equations
    v2=v1 + a x t & v2(square root)=v1(square root) + 2ad

    3. The attempt at a solution
    I tried 30km/h into the second equation (knowing that acceleration in 9.81) and that the vertical at its peak is 0 but my number is no were near the answer key

    do i have to convert km/h to m? and where did i go wrong
  2. jcsd
  3. May 25, 2016 #2


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    Gold Member

    How can we tell where you went wrong when you don't show your work? You could be making a simple math error.
  4. May 25, 2016 #3
    i did v2=0 v1=30km/hr + 2 x 9.81 (d)
    i square rooted 30 to get 900 + 2 x 9.81 to get 919.62 which is far off from the answer i need
  5. May 25, 2016 #4
    to answer your other question, you have to make sure all your units agree. Km/h is not the same as m/s^2 (which is what the acceleration due to gravity is in, I am assuming). Units of length must agree and units of time must agree.
  6. May 25, 2016 #5
    the answer is in meters, which is 3.54m. So i do not convert km to m i convert to degrees?
  7. May 25, 2016 #6
    Convert km/h into the same units as your acceleration - so if using 9.81m/s2 convert km/h into m/s. You are only dealing with one direction so there isn't a reason to apply any conversion of degrees.
  8. May 25, 2016 #7
    thanks i did D= v2 - V1/2 X a

    so i did 0-8.3 (Square root)/2 x 9.81

    then i did 68.8/19.62 got 3.51m

    does that seem right ^^
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