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Homework Help: Finding velocity when onlu a mass and acceleration is given

  1. Nov 18, 2011 #1
    1. The problem statement, all variables and given/known data
    The instruments attached to a weather balloon have a mass of 5.0kg.The balloon is released and exerts an upward force of 98 N on the instruments. I have found that the acceleration is 1.96 m/s/s by F=ma.
    After the balloons have accelerated for 10 seconds, the instruments are released. What is the velocity of the instruments at the moment of their release?

    2. Relevant equations
    V(sub f)^2=V(sub i)^2 + 2ad
    I have tried this but I don't know either velocity or the distance.
    or would it be:
    V(sub f) = V(sub i) +at

    3. The attempt at a solution
    V(sub f)^2= 0^2 + (2)(1.96m/s^2)(d)
    V(sub f)= 0 + (1.96m/s^2)(10s)
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 18, 2011 #2


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    Gold Member

    Be careful, that's not the acceleration. How did you figure out what the acceleration was?

    Once you know the acceleration, you also know that

    [itex]v = v_0 + at[/itex]

    It's assumed to be released from rest, so [itex]v_0 = 0[/itex]. It's a simple matter of letting [itex]t = 10 sec[/itex]. Remember, the question is quite simple since it only asks for what happens at the release.
  4. Nov 18, 2011 #3
    Oh okay. I looked at the calculator wrong for the decimal. So the initial velocity is 0?
  5. Nov 18, 2011 #4
    The force exerted by the balloon on the instruments is 98N, but what is the net force after accounting for gravity?
  6. Nov 18, 2011 #5
    is it 10?
  7. Nov 18, 2011 #6
    How did you arrive at that? E.G. which equation did you use?
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