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Homework Help: Artificial Gravity on a Spinning Spaceship - Find the Period

  1. Aug 16, 2012 #1
    1. The problem statement, all variables and given/known data
    Spinning Space Ship
    One way to provide artificial gravity (i.e., a feeling of weight) on long space voyages is to separate a spacecraft into two parts at the ends of a long cable, and set them rotating around each other. A craft has been separated into two parts with a mass of 86000 kg each, at the ends of a cable with their centers of mass 106 m apart, rotating around the center point of the cable with a period of 232.2 seconds.

    If the cable is reeled in so that the the centers of the two pieces are now only 74.2 m apart, what will the new period be?

    2. Relevant equations
    T = 1/f or f = 1/T
    ω = 2*pi*f
    L = I*ω
    I = Ʃ m*r^2
    L(initial) = L(final)

    3. The attempt at a solution
    First, I noted that this scenario should follow the principle of conservation of angualr momentum. Therefore L(initial) = L(final) should be true. Then, I followed this series of steps...

    L = I*ω
    L = (Ʃ m*r^2)*ω
    L = (2*(m*r^2))*ω
    L = (2*(m*r^2))*2*pi*f
    L = (2*(m*r^2))*2*pi*1/T

    Upon finding this initial angular momentum, I thought I could find the final L by setting this expression equal to L(final) with the new radius to the axis point and with T set as an unknown variable.

    Please let me know if this is on the right track? I am a little bit hesitant about it so any feedback would be awesome.
  2. jcsd
  3. Aug 16, 2012 #2


    User Avatar
    Homework Helper

    it looks good to me, keep on with it :)
  4. Aug 16, 2012 #3
    Thanks Batman! (Haha, referring to your username, Bruce W.). I was wondering if you could help me with the second part of the question. I am stumped.

    The two pieces of the spacecraft are returned to their initial configuration with a period of 232.2 seconds. A radiation leak is detected in one of the engines. An escape pod from each section of the spacecraft are ejected as indicated in the figure. Notice that the direction of rotation for the two pieces of the spacecraft is also indicated in the figure.
    (One of the pods is rotating into the page and the other is rotating out of the page).

    Escape Pods
    The escape pods each have a mass of 12000 kg and are ejected with a speed of 77.99 m/s along thedirections indicated in the figure with θ = 32.5 degrees.
    What is the new period of the remaining spacecraft after the two escape pods are ejected?

    I was initially just trying to use conservation of angular momentum to solve this problem (as I did in the first part). However, I got confused because they provide us with a speed and a direction for the escape pods?
  5. Nov 10, 2013 #4
    I have this same problem and can't find the new period of the remaining spacecrafts after the escape pods are ejected. Did you ever figure out how to do this?
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