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: Rotational Dynamics

  1. Nov 13, 2004 #1
    I have a problem dealing with torques and acceleration. I am sure I solved it right but when submitting the answers, I get the response "Incorrect" :cry:

    The problem:

    A wheel of radius 2 m, mass 53 kg, and moment of inertia (3/4) (53 kg) (2m)^2 about the center of mass is mounted on a frictionless horizontal axle.
    (g = 9.8). A light cord wrapped around the wheel supports an object of mass 106 kg. The weight is released from rest at the level of A and falls a distance h, past level B (AB=28 m). a) Find the velocity as it passes B b) Determine the tension of the string.

    I set up everything.

    Torque = I* alpha = T*R since alpha = a/R and we know I, conclusion is T=42*a

    Then: T=m(g - a): putting T from above, I got a=7.0189189 m/s^2
    To find V as the mass passes point B: Vf^2 = 2*a*28m ---> and v at B = 19.83 m/s. This was OK

    For b) I used T=m(g-a), since I know a = 7.0189189m/s^2 , I substituted it at the equation and I got T= 294.79 N but this is not the right answer.

    Maybe I can use I*alpha = T*R and from that get T because everything is known, but I am not sure. Any suggestions?
  2. jcsd
  3. Nov 13, 2004 #2
    Can anyone help?
  4. Nov 13, 2004 #3
    For part a)

    For part b)

    Do these things help?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook