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Angular Velocity Dynamics (Easy?)

  • Thread starter Stingarov
  • Start date
22
0
A 73.9 kg shaft with a radius of 8.9 cm is spinning at a rate of 364.5 rpm. If a board leans against the outside providing a frictional force of 59.92 N, how long will it take for the shaft to stop rotating?

Answer says 2.094 s.

Problem I have is that my Inertia table doesn't list shaft inertia or anything. Unsure how to go about starting this?
 
Last edited:

Doc Al

Mentor
44,810
1,074
Treat the shaft as a cylinder--see if that works.
 
22
0
So Inertia = Solid cylinder = 1/2mr squared.
I = .5 * 73.9 * .089 sq
I = .293

Do I use the Net Torque = 0 from here? I'm still pretty lost for some reason from here.
 
22
0
Alright I figured it out surprisingly by conceptual thinking.

Force: I/r
1) 1/2mr = 3.28855
2) * angular velocity = 3.28855 * 38.17 radians per second

3) 125.52 / F2 = time
= 2.094
 

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