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Falling Object

  1. Sep 14, 2010 #1
    1. The problem statement, all variables and given/known data
    A helicopter is ascending vertically with a speed of 5.83 m/s. At a height of 121 m above the Earth, a package is dropped from a window. How much time does it take for the package to reach the ground?


    2. Relevant equations
    Vfinal=Vinitial + at
    or
    Xfinal=Xinitial + Vinitial(t) + (1/2at)squared


    3. The attempt at a solution
    I tried putting in my answer from the first equation but it was wrong, and every time I try the second equation I get a negative answer which doesn't make sense.
     
  2. jcsd
  3. Sep 14, 2010 #2
    negative time in physics doesn't really mean anything. all the negative means is that you put a negative -9.8 acceleration for gravity

    the problem gives you this data:

    d = 121m
    vi = 5.83 m/s (initial velocity is 5.83 meters per second. yes it is negative since it's going down but we aren't going to worry about it)
    a = 9.8m/s^2
    t = ?

    so you use this equation:
    d= vi + 0.5at^2
    121 = 5.83+.5*9.8*t^2
    t = 4.8481 seconds
     
  4. Sep 14, 2010 #3
    My online homework say's that's not correct. I'm also confused on how you derived your equation?
     
  5. Sep 14, 2010 #4
    well i found out the velocity at the time of collision 1st with v^2 =vi^2 +2a(x-xi) to be 49.05 and then using the 1st equation i got the time to be 5.6 or 5.599

    edit: if your homework was anything like mine then it was probably asking for that too and i found it easier to get that answer 1st
     
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