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: Rigid Object Under Torque

  1. Apr 10, 2008 #1
    A grinding wheel is in the form of a uniform solid disk of radius 7cm and mass 2kg. It starts from rest and accelerates uniformly under the action of the constant torque of 0.6 Nm the motor exerts on the wheel. a) How long does the wheel take to reach its final operational speed of 1200 rev/min? b) Through how many revoulutions does it turn?

    Torque= (m*r^2)*circular accel.
    circular veloc. Final= circ.veloc. Intial + circular accel.*time

    Ok, so I tried to use the above torque equation to solve for circular acceleration. So, .6/(2*.07^2) = circular accel.= 61.22 rad/s. Then I tried putting that value back into the other equation. So, 125.66 rad/s(I converted it)-0=61.22*t. Thus, t=2.06s. However, the time I am supposed to get is 1.03s (half of what I got). Could someone please explain where I went wrong?
  2. jcsd
  3. Apr 10, 2008 #2
    the equation for torque is [tex]\tau=I\alpha[/tex], and for a disk rotating about its axis, [tex]I=\frac{1}{2}MR^2[/tex].

    i think that should solve your problem. cheers
  4. Apr 10, 2008 #3
    Thank you that solved the problem!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook