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!

Maximum Kinetic Energy from a Physical Pendulum

  1. Jan 17, 2016 #1
    1. The problem statement, all variables and given/known data
    Determine the maximum kinetic energy of a uniform rod of mass 0.5Kg and length 0.75 that has an angular displacement of 5 degrees.

    2. Relevant equations
    y = rsin (x) where x is the angular displacement

    3. The attempt at a solution
    Using conservation of energy ETotal = EMech + EPOTENTIAL

    Kinetic energy is at a maximum when all potential energy is converted to kinetic energy

    Centre of mass of of physical pendulum is equal to L/2

    Therefore max kinetic energy = mg (l/2) sin (x)
    = 0.0163417 J

    I just have no idea if this is right
     
  2. jcsd
  3. Jan 17, 2016 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Did you mean to write EKinetic instead of EMech?

    Can you explain why you used a factor of sin(x) here? Be sure to draw a picture to help find the change in vertical height of the center of the rod.
     
  4. Jan 17, 2016 #3
    I used a factor of sin (x) because the change in the y axis * mg is equal to total potential energy
    y = r sin (theta) when changing between polar and cartesian coordinates
    Is this the wrong way to think about it?
     
  5. Jan 17, 2016 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member

    First of all, I want to make sure I'm interpreting the question correctly. I assume from the title that you are dealing with a swinging physical pendulum. I am also assuming that the maximum angular displacement from equilibrium is 5 degrees. Is this correct?
     
  6. Jan 17, 2016 #4
    Would I have to use cos (x) instead of sin (x)?

    Umm yes thats the question :)
     
  7. Jan 17, 2016 #5

    TSny

    User Avatar
    Homework Helper
    Gold Member

    It's not a matter of just replacing sin(x) by cos(x). Did you draw a picture?
     
  8. Jan 17, 2016 #6
    Okay, so i drew a picture and realised that I made a mistake.

    I got to
    Change in x = l/2 * (1- cos(x))
     
  9. Jan 17, 2016 #7

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Looks good. But you're using x for two different things!
     
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: Maximum Kinetic Energy from a Physical Pendulum
Loading...