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Homework Help: Vibration of a cantilever beam

  1. Jun 5, 2017 #1
    1. The problem statement, all variables and given/known data
    A rectangular cantilever beam of length L and side lengths b with negligible mass is attached horizontally to a wall. A mass m is attached to the end of the beam where a motor is also located. The motor applies a force on the end of the beam described by the equation P*sin(w*t).

    Derive an expression for the vertical vibration of the mass m, that is, find x(t) for a stable solution.

    2. Relevant equations
    k = 3EI / L^3
    I = b^4/12

    3. The attempt at a solution
    I'm at a loss here. I am unaware of any equation that describes the damping in a cantilever beam. I want to set up the problem as

    x'' + c/m x' + k/m x = Psin(wt)/m

    which is how I usually solve these types of problems. But I'm at a loss when it comes to finding out how to express c. Furthermore, when it says to find a stable solution, is it hinting towards harmonic motion?
  2. jcsd
  3. Jun 5, 2017 #2
    Perhaps they mean that it is simple harmonic motion without damping?
  4. Jun 5, 2017 #3


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    Science Advisor
    Homework Helper
    Gold Member

    Yes, it is forced, undamped.
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