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Homework Help: Spring Rotational Problem

  1. Nov 12, 2013 #1
    1. The problem statement, all variables and given/known data
    Four masses M in deep space are connected by four identical light springs with spring constant k and equilibrium length L. The four mass, four spring assembly is square and lies in a plane; all four masses are rotating with ω =√(k/M), in uniform circular motion about an axis perpendicular to the plane and equidistant from all four masses. What is the kinetic energy of this system?

    2. Relevant equations
    3. The attempt at a solution
    ITotal=4MR2 where R is the distance to mass when the masses are rotating. R should be large that L because the springs will stretch when the system is in motion.
    I feel like this is incomplete especially with respect to Δl. Is there any other way to put it. I was thinking of maybe finding what Δl maybe using Hooke's Law but I don't know how to go about that. I was thinking of equating it to the centripetal force. Please let me know and thank you in advance
  2. jcsd
  3. Nov 12, 2013 #2

    Doc Al

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    Staff: Mentor

    You're on the right track.

    Combine Newton's 2nd law with Hooke's law. Draw a diagram of the forces acting on each mass.
  4. Nov 12, 2013 #3


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    Staff: Mentor

    Yes, use the centripetal force. The springs meet at each corner of the square and their tensions add vector-wise to make up the centripetal force. You can find an expression for the radial distance of the masses that way.
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