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: Car problem-rotational motion?

  1. Mar 17, 2010 #1
    1. The problem statement, all variables and given/known data
    The 1900 kg mass of a car includes four tires, each of mass (including wheels) 40 kg and diameter 0.80 m. Assume each tire and wheel combination acts as a solid cylinder.
    (a) Determine the total kinetic energy of the car when traveling 60 km/h.


    (b) Determine the fraction of the kinetic energy in the tires and wheels.
    %

    (c) If the car is initially at rest and is then pulled by a tow truck with a force of 2500 N, what is the acceleration of the car? Ignore frictional losses.


    (d) What percent error would you make in part (c) if you ignored the rotational inertia of the tires and wheels?


    2. Relevant equations
    I would understand where to go in step two. For step 1 i was using K=1/2 mv^2
    For step 3 i used F=ma. Apparantly Im totally wrong.

    3. The attempt at a solution
    Help. The formulas I use are giving me incorrect results. about 200,000 J is what I got
     
  2. jcsd
  3. Mar 18, 2010 #2

    phyzguy

    User Avatar
    Science Advisor

    You're forgetting the rotational kinetic energy stored in the rotation of the wheels. In addition to the [tex]\frac{mv^2}{2}[/tex] there should be a [tex]\frac{I\omega^2}{2}[/tex] term.
     
  4. Mar 18, 2010 #3
    the rotational kinetic energy can be found from
    I=1/2*40*4*.4^2?
    and
    60*1000/3600=v
    omega=v/0.4?
     
  5. Mar 18, 2010 #4
    check that. I was able to solve part a)..thankyou!
    I do not even know how to start on the next 3 parts..if you could point me where to go I would be indebted.

    wouldnt b simply be to divide the rotational Kinetic energy by the total kinetic energy? apparantly not..
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook




Loading...
Similar Threads for problem rotational motion Date
Rotational Motion and Torque problem Mar 21, 2018
Rotational Motion Problem Jul 29, 2017
Have a problem with this Rotational Motion question Jun 19, 2017
Center of mass on plank problem Mar 21, 2017