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Momentum questions-please help-need them done tonight

  1. Feb 3, 2005 #1
    Please help with the following 3 questions:

    1. A group of playful astronauts each with a bag full of balls, form a circle as they free fall in space. Describe what happens when they begin tossing the balls simultaneously to one another.

    Due to absence of gravitation, wouldn't the balls be floating away - but this seems to be a laymans answer and I do not think its correct.

    2. A 5-kg fish swimming 1 m/s swallows an absent minded 1 kg fish at rest. What is the speed of the larger fish immediately after lunch? What would its speed be if the small fish were swimming toward it at 4 m/s?

    After lunch:
    m(1)=5 kg, v(1)=1 m/s, m(2)=1 kg, v(2)=0

    (5)(1) + (1)(0)
    --------------- = 5/6 m/s
    (5)+(1)

    If small fish swimming toward it at 4 m/s:

    m(1)=5 kg, v(1)=1 m/s, m(2)=1 kg, v(2)=-4 m/s (swimming towards it)

    (5)(1) + (1)(-4)
    --------------- = 1/6 m/s
    (5)+(1)

    3. Comic strip hero Superman meets an asteroid in outer space and hurls it at 100 m/s. The asteroid is on thousand times more massive than superman is. In the strip, superman is seen at rest after the throw. Taking physics into account, what would be his recoil speed?

    This question has been asked before by someone else but no answer given, please HELP!

    Thanks
     
  2. jcsd
  3. Feb 3, 2005 #2
    For #3, im assuming asteroid is at rest. So
    Hero
    [itex]
    m_{H}= m
    [/itex]
    [itex]
    v_{iH}= 0 m/s
    [/itex]
    Asteroid
    [itex]
    m_{A}= 1000m
    [/itex]
    [itex]
    v_{iA}= 0 m/s
    [/itex]
    [itex]
    v_{fA}= 100 m/s
    [/itex]
    So momentum before = momentum after
    [itex]
    0 = m_{A}v_{fA} + m_{H}v_{fH}
    [/itex]
     
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