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Homework Help: Space Station,Exploding Object

  1. May 17, 2012 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    I solved questions a) and b) no problem but the thing is that in c)

    i said that B will hit the end first so at first the tube will move with a speed Vtube1 ( Vb=x/t).So t=23.25s . After some time which i found to be 47.17 s , object A will hit the other end so the tube will now move by δV = Va-Vb .

    But in the solutions it says that the tube's velocity will be zero!!!

    can you please explain ?!

    Attached Files:

  2. jcsd
  3. May 17, 2012 #2


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    Hi ZxcvbnM2000! :smile:
    How can it take 23 s to go only 1 m ? :confused:

    A will hit first.

    (It would help in future if you show all your calculations at the start.)
    what about conservation of momentum?
  4. May 17, 2012 #3
    Explosion (system of objects A&B) : 0 = 0.8*1 + 3* ub so ub = -0.26 m/s .

    Object A : Ma*ua = (Ma+Mtube)*Vtube <=> Vtube = 0.0615 m/s

    Object B : Mb*ub=(Mb+Mtube)*V'tube so V'tube=-0.052 m/s

    And because this is space we're talking about the movement is linear so V=x/t for each object and we can find the times until they hit the ends.

    What do you mean conservation of momentum ?
    This is really not intuitive for me!

    So you are saying that if we consider the tube as system how can we prove that it won't move ?
  5. May 17, 2012 #4


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    A yes; B no, because you need to use the new velocity and mass after A collides with the tube
    if we consider the whole thing as the system, yes :smile:
  6. May 17, 2012 #5
    Momentum Conservation between ( A&Tube) & B

    so mb*ub + (ma + mtube)*V = (ma +mb +mtube)*V'

    but we know that ma*ua + 0 =(ma +mtube)*V , also -maua=mbub

    so V' = 0 right ?? So it won't move.

    But i have a question as The tube is going to the left after colliding with A and B is going to the right doesnt this mean that B will cover less distance ??
  7. May 18, 2012 #6


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    quicker would be to compare before and after for the whole thing :wink:
    yes, but so what? it won't affect the velocities, and the question doesn't ask for it! :smile:
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