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Homework Help: Simple Kinematics

  1. Sep 19, 2008 #1
    1. The problem statement, all variables and given/known data

    A hot air balloon is traveling vertically upward at a constant speed of 4.4 m/s. When it is 27 m above the ground, a package is released from the balloon.

    The acceleration of gravity is 9.8 m/s^2.

    a) After it is released, for how long is the package in the air.

    b) What is its speed just before impact with the ground?

    2. Relevant equations

    x = x0 + v0t + 1/2at^2

    v = v0 + at

    3. The attempt at a solution

    a)

    0 = 27 + 4.4t + 1/2(-9.8)t^2
    t = 2.839 s ***this answer is wrong.

    Is it wrong because v0 should equal 0 and not 4.4?

    b)

    v = 4.4 - 9.8(2.839)
    v = -23.42 m/s ***this answer is obviously wrong because t is wrong.

    But, should v0 be zero in this case as well?
     
  2. jcsd
  3. Sep 19, 2008 #2
    I don't see anything wrong with your algebra in part (a) and (b). The only problem I see is your rounding of sig figs.
     
  4. Sep 19, 2008 #3
    Sig figs don't matter in the answer. In fact, answers are encouraged to be 6 figures long (though less is still acceptable).

    But you don't agree that v0 = 0 in this problem?
     
  5. Sep 19, 2008 #4
    The package does indeed have an initial velocity of 4.4m/s if you are measuring it from the ground which it seems the problem is doing throughout.

    What would make you think otherwise?
     
  6. Sep 19, 2008 #5
    No, I agree with you. It's just, I'm still being told it's the wrong answer. But thank you for your help.
     
  7. Sep 19, 2008 #6
    Who or what is telling you it is wrong? Are you doing one of those buggy web assignment things?
     
  8. Sep 19, 2008 #7
    Yes, it's a web assignment. But, like you said, the problem is set up correctly?

    So, I'm guessing it's a tech problem. Again, thanks for the help.
     
  9. Sep 19, 2008 #8
    Do you have to input both answers in the same line? The problem might be the fact that part b asks for the speed and you are giving the velocity.
     
  10. Sep 21, 2008 #9
    is answer 1.94s
     
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