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!

Energy and Rotational Motion

  1. May 6, 2013 #1
    1. The problem statement, all variables and given/known data
    We performed a small experiment in class which had us attach a mass to a string which hung on a pulley which led to a rotating object.
    D5TKaV7.png
    We were then told to write down a conservation of energy equation stating that the initial energy is equal to the final energy. We were asked to include kinetic energy (rotational, translational), potential energy, and energy lost due to friction which we found with Tf=f*r.


    2. Relevant equations


    3. The attempt at a solution

    This is what I have setup so far.

    Ui +Kroti +Ktransi=Uf+Krotf +Ktransf +Wf

    mgd=.5Iw^2 + .5mv^2 -f

    I'm still a little confused about how energy is conserved if we're losing energy due to friction?

    After that they ask me to replace every instance of w with v/r and v with 2d/t and try to get the following I=(mr^2)((gt^2/2d)-1-(t^2/(2md))f)

    What am I doing wrong here?
     
  2. jcsd
  3. May 6, 2013 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    f is the force of friction? If so, there are two things wrong with the -f term.
     
  4. May 6, 2013 #3
    how in the world are you equating torque with energy
     
  5. May 6, 2013 #4
    I suppose I should have did f*Δd? I'm not sure what to do here.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Energy and Rotational Motion
Loading...