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: Periodic Motion question

  1. Apr 8, 2005 #1
    Here is my problem:
    A hard-boiled egg of mass 45.0 g moves on the end of a spring with force constant k = 24.7 N/m. Its initial displacement is 0.290 m. A damping force F = - bv acts on the egg, and the amplitude of the motion decreases to 0.120 m in a time of 5.10 s.

    I need to find the magnitude of the dampening constant b.

    I am completely clueless on how to approach this question.

    edit: corrected some stuff.
    Last edited: Apr 8, 2005
  2. jcsd
  3. Apr 8, 2005 #2
    Me too, since I do not know what you mean by 'the force of B'.
  4. Apr 8, 2005 #3
    sorry i guess i typed it wrong. the dampening force:

    F = -bv

    I need to find the magnitude of the dampening constant b.
  5. Apr 8, 2005 #4
    [tex] x(t) = x_{m} e^{\frac{-bt}{2m}} cos( \omega t) [/tex]

    where Xm is the initial displacement
    b is hte damping force
    m is the mass
    omega is the angular frequency [tex] \omega = \frac{2 \pi}{T} [/tex] where [tex] T = 2 \pi \sqrt{\frac{m}{k}} [/tex]
  6. Apr 8, 2005 #5
    for some reason that is not working for me.
  7. Apr 8, 2005 #6
    perhaps you are not using your numbers correctly

    initla displacement Xm = 0.290 m
    k = 24.7 N/m
    X(5.10) = 0.120 m
    t = 5.10s
    m = 45g = 0.045 kg
    and omega = [itex] \sqrt{\frac{m}{k}} [/itex]
    it's blind substitution, really
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook