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: Rod - angular acceleration

  1. Feb 24, 2005 #1
    rod -- angular acceleration

    A long uniform rod length L and mass M is pivoted about a horizonal, frictionless pin passing through one end. The rod is released from rest in a vertical position. The instant the rod is horizontal, what is the magnitue of its angular acceleration.

    It's angular speed I know is [tex]\sqrt{\frac{3g}{L}}[/tex]
    using the formula [tex]\alpha=rw^2[/tex]
    I get then angular acceleration to be 3g. However the book tells me that the answer is 3g/2L. What am I missing?
  2. jcsd
  3. Feb 24, 2005 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Whatever formulas are you using???

    Write down the moment-of-momentum equation about the pivot:
    a) What is the moment of inertia?
    b) What is the torque induced by gravity?
  4. Feb 24, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper

    Yes,your answer is incorrect,even not knowing the physics to solve the problem,nor the book's answer.

    I think you can use the law of conservation of energy...

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook