1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Torque to rotate spinning gyroscope

  1. Dec 2, 2011 #1
    1. The problem statement, all variables and given/known data
    The Hubble Space Telescope is stabilized to within an angle of about 2 millionths of a degree by means of a series of gyroscopes that spin at 1.92×104 . Although the structure of these gyroscopes is actually quite complex, we can model each of the gyroscopes as a thin-walled cylinder of mass 2.00 and diameter 5.00 , spinning about its central axis.
    How large a torque would it take to cause these gyroscopes to precess through an angle of 1.30×10−6 degree during a 5.00 hour exposure of a galaxy?

    2. Relevant equations
    torque = Ω*L

    3. The attempt at a solution



    Δt=5 hours

    torque = Ω*I*ω
    =4.1*10^-8 Nm

    This is the wrong answer and I feel as if the torque shold be rather larger by intuition. Any help would be appreciated.

    Edit: 3.17*10^-12 Nm turned out to be the correct answer, but i'd still like to know how to do this question.
    Last edited: Dec 2, 2011
  2. jcsd
  3. Dec 3, 2011 #2
    Check this again:
  4. Dec 3, 2011 #3
    sorry, i made a mistake in my original post, the given angle is 1.3^-6deg.

    ok, so now i get

  5. Dec 21, 2011 #4
    I think 1.27*10^-11 is not the correct answer , how is the question being solved in the correct way ?
  6. Nov 24, 2012 #5
    The problem with your solution, in case you are still wondering,
    is I= mr^2
    not I=md^2
    therefore you take the diameter of 5 divide it by 2.
    So I=2(0.025^2)
    and that would be the last error after the conversion of degrees to radians which you fixed.
    I just had to do the same problem so I decided to answer your question.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook