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Homework Help: Simple Pendulum Motion and Physical Pendulum

  1. May 27, 2007 #1
    1. The problem statement, all variables and given/known data
    1) Find the period of a pendulum 50 cm long when it is suspended in (a) a stationary elevator; (b) an elevator falling at the constant speed of 5.0 m/s; (c) an elevator falling at the constant acceleration of 2.0 m/s2; (d) an elevator rising at the constant speed of 5.0 m/s; (e) an elevator rising at the constant acceleration of 2.0 m/s2.

    2. Relevant equations
    Period = 2 pi Squareroot of Length of arm/ Gravity

    3. The attempt at a solution
    1) I could solve a) by simply replacing data into the formula, but im not sure how does the change in velocity and acceleration affects the data that is where im stuck at.
    Last edited: May 27, 2007
  2. jcsd
  3. May 27, 2007 #2


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    Gold Member

    A force has to be introduced to change the period.

    Constant motion doesn't introduce force, only acceleration does.
  4. May 27, 2007 #3
    so that means that when the velocity is up or down 5m/s constat there is no acceleartion, so only G is taken into account???
    but for the toher two, how are they calculated?
  5. May 27, 2007 #4


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    Gold Member

    Gravity is an acceleration... the period is actually

    P = 2*pi*sqrt(L/a)

    where a is acceleration.

    Gravity is always there, but in acceleration situations a will not simply be equal to G as it is in the stationary and constant motion situation.
  6. May 27, 2007 #5
    Yes i understand that part, but what i don't know is how does the up and down acceleration influence the total acceleration, this is just a hunch but i think that when acceleration is downward i would be 7.81, and when it is upward it will be 11.81, im not totally sure about that
    As for the ones where velocity is constant i think that the only acceleration acting is gravity, and im not sure of that either..
  7. May 27, 2007 #6

    Doc Al

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    Staff: Mentor

    You are correct. The acceleration of the elevator adds (or subtracts) from the standard acceleration due to gravity (9.81 m/s^2).
  8. May 27, 2007 #7
    ok thanks very much
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