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Math Help - Am I following this right??

  1. #1
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    Am I following this right??

    Hi, Stuck on this one, I have a drawing but it does not make sense.
    Is this 1D or 2D kinematics??

    a hot air balloon is rising straight up with a speed of 3.0 m/s. A ballast bag is released from rest relative to the balloon when it is 9.5 m above the ground.

    How much time elapses before the ballast bag hits the ground.
    So I have Vo = 0 m/s as it's from rest relative to the balloon?? is that correct.
    a = -9.8 m/ss
    d = 9.5 m

    Do I use d = Vot + 1/2 at^2. And if so how to do I get the 2 t's into 1. I tried to re arrange and it's not working out.

    Please help me start this please, thanks. Tell me if I am on the right track.
    Jo
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  2. #2
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    Quote Originally Posted by bradycat View Post
    Hi, Stuck on this one, I have a drawing but it does not make sense.
    Is this 1D or 2D kinematics??

    a hot air balloon is rising straight up with a speed of 3.0 m/s. A ballast bag is released from rest relative to the balloon when it is 9.5 m above the ground.

    How much time elapses before the ballast bag hits the ground.
    So I have Vo = 0 m/s as it's from rest relative to the balloon?? is that correct.
    a = -9.8 m/ss
    d = 9.5 m

    Do I use d = Vot + 1/2 at^2. And if so how to do I get the 2 t's into 1. I tried to re arrange and it's not working out.

    Please help me start this please, thanks. Tell me if I am on the right track.
    Jo
    Take down as positive:

    u = -3 m/s
    d = 9.5 m
    a = 9.8 m/s^2
    t = ?

    Think about these values. In particular, think about the sign they have and think about why u is not equal to zero.

    Then use the appropriate formula for uniform straight line motion.
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  3. #3
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    So the u above is Vo??
    Not use to that letter for something, or what do you label it as?
    Because it's relative to the balloon, anything going down, that was negative, is now positive then??
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  4. #4
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    Quote Originally Posted by bradycat View Post
    So the u above is Vo??
    Not use to that letter for something, or what do you label it as?
    Because it's relative to the balloon, anything going down, that was negative, is now positive then??
    Yes, my u is your Vo.

    If you take up as positive (which is what you seem to want to do) and note that the origin is the balloon at the time of release (I took this as the origin in my previous reply too but assumed you realised this) , then:

    u = 3 m/s
    d = -9.5 m
    a = -9.8 m/s^2
    t = ?

    Note: It seems you might need to spend more than 8 minutes doing the thinking I suggested that you do.
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  5. #5
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    Hey Mr,
    I was not getting something, but now I understand. I had to find V, then with that I can input it into V=Vo+at and I got an answer of 1.7s.
    Thank you. This is still fairly new to me, and to understand, evening reading out of my book, has me a bit confused. thank you again.
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