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!

Kinetic Energy of Rotation

  1. Mar 28, 2010 #1
    1. The problem statement, all variables and given/known data

    An automobile is traveling at v = 32 m/s and has wheels with radius R = 22 cm. Assuming that the wheels are disks which roll without slipping and have a mass m = 11 kg, what is the kinetic energy of rotation of the four tires in Joules?


    2. Relevant equations

    w = v/R

    The kinetic energy for each tire is then


    KE = 1/2 Iw^2

    There are four wheels.

    3. The attempt at a solution

    I tried converting 32 m/s to rad/s for angular velocity. So 32m/s divided by .22m (radius) to get 145.45.


    Then I squared that answer. I multiplied it by .5.

    Then for I, I used mr^2 and got .5324.

    I got 5631.648. Tried multiplying that by four and it didn't work.

    I've tried entering

    3 Incorrect. (Try 1) 5630
    5 Incorrect. (Try 2) 5.6x10^2
    7 Incorrect. (Try 3) 2.3x10^4
    9 Incorrect. (Try 4) 22500


    None of these were correct. I'm wondering where I messed up....
     
  2. jcsd
  3. Mar 29, 2010 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    "Then for I, I used mr^2 and got .5324."

    The wheels were assumed disks, and the moment of inertia of a disk is 0.5 mr^2.

    ehild
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook