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Homework Help: Free fall acceleration

  1. Sep 18, 2007 #1
    1. The problem statement, all variables and given/known data
    A hot-air balloon is ascending at the rate of 13 m/s and is 90 m above the ground when a package is dropped over the side.

    (a) How long does the package take to reach the ground?

    (b) With what speed does it hit the ground?

    2. Relevant equations

    3. The attempt at a solution

    Tried 2a[tex]\Delta[/tex]y=Vf[tex]^{2}[/tex]-vi[tex]^{2}[/tex]

    I don't know if the initial velocity is 0 or 13m/s
  2. jcsd
  3. Sep 18, 2007 #2


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    If the balloon is ascending at 13m/s, then vi=13m/s (with the sign convention that upwards is positive). Try using the equation y=vi*t+0.5a*t^2.
  4. Sep 18, 2007 #3
    thanks, got part a right.

    for b, i'm getting 42.18. is that right and would it be negative if it is going down?
    used vf= vi + a*t and vf^2=vi^2+2*a*d
  5. Sep 18, 2007 #4


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    Yes and yes; although you only need to use the second equation.
  6. Sep 18, 2007 #5
    ty got it right
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