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: Angular frequency of plank attached to spring

  1. Feb 25, 2016 #1
    1. The problem statement, all variables and given/known data
    A horizontal plank (mass 2kg, length 1m) is pivoted at one end. A spring (k=1000N/m) is attached at the other end. Find the angular frequency for small oscillations.

    Answer: ω=39rad/s

    2. Relevant equations
    ω = √(mgd + kΔxd/I)
    I think I would be treating the plank as a long thin rod with rotational axis through the end (since I'm not provided with the dimensions of the plank), so I = 1/3mL2 + md2
    Where L: length of the rod, d: distance between pivot and rod's centre of mass (d=L/2)

    3. The attempt at a solution
    I = 1/3mL2 + md2 = 1/3mL2 + m(L/2)2

    ω = √(mgd + kΔxd/I)
    mgd component --> mg(L/2)
    kΔxd component --> mg(L/2)2

    Substituting all the known values...
    ω = √[(2)(9.8)(1/2) + 1000(12)] / [(1/3)(2)(12) + 2(1/2)2]
    ω = √1009.8/1.16 = 29.4

    Still not getting the correct answer.

    Attached Files:

  2. jcsd
  3. Feb 25, 2016 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Not so.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted