1. Not finding help here? Sign up for a free 30min 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!

Rotational motion, energy conservation problem please help

  1. Nov 16, 2011 #1
    rotational motion, energy conservation problem URGENT please help

    1. The problem statement, all variables and given/known data

    A uniform rod of mass M=2 kg and length L = 2m is pivoted from its end. It has a point mass m=1 kg on its tip. It stars from rest at an angle of 30 degrees above horizontal. It falls under the influence of gravity. How fast is the tip m moving when the rod is horizontal at θ
    = 0
    2. Relevant equations

    mgh = 1/2mv^2

    3. The attempt at a solution

    h= Lsinθ = 1
    m cancels from both sides
    so you're left with
    v=√2g=4.42

    BUT, the actual answer given is 4.8

    Help please! I have a test in just a few hours and have been trying to figure this problem out for awhile! Thanks
     
  2. jcsd
  3. Nov 16, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Re: rotational motion, energy conservation problem URGENT please help

    How would you write the rotational KE of the system? Also, what's the total change in gravitational PE as it falls?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook