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Rotational Inertia of Pulley, Integration Help!

  • Thread starter rmunoz
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Homework Statement



A pulley, with a rotational inertia of 1.5 10-3 kg·m2 about its axle and a radius of 21 cm, is acted on by a force applied tangentially at its rim. The force magnitude varies in time as F = 0.50t + 0.30t[tex]^{2}[/tex], where F is in newtons and t in seconds. The pulley is initially at rest.

(a) At t = 10.0 s what is its angular acceleration?
rad/s2


(b) At t = 10.0 s what is its angular velocity?
rad/s




Homework Equations


Tnet=I[tex]\alpha[/tex]

f=.50t + .30t[tex]^{2}[/tex]

The Attempt at a Solution


I allready got the acceleration for the pulley. It turned out to be 4900 rad/sec. But now i assume because the amount of force is reliant on the time (in other words, is accelerating at a non-constant rate), some integration will be needed. The problem for me is, i have only the vaguest idea of how to actually integrate. Would anyone mind helping me with this problem if it does in fact require integration, by showing me the exact steps? And if that is not the case, perhaps point me in the right direction?
 

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  • #2
LowlyPion
Homework Helper
3,090
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Homework Statement



A pulley, with a rotational inertia of 1.5 10-3 kg·m2 about its axle and a radius of 21 cm, is acted on by a force applied tangentially at its rim. The force magnitude varies in time as F = 0.50t + 0.30t[tex]^{2}[/tex], where F is in newtons and t in seconds. The pulley is initially at rest.

(a) At t = 10.0 s what is its angular acceleration?
rad/s2

(b) At t = 10.0 s what is its angular velocity?
rad/s


Homework Equations


Tnet=I[tex]\alpha[/tex]

f=.50t + .30t[tex]^{2}[/tex]

The Attempt at a Solution


I allready got the acceleration for the pulley. It turned out to be 4900 rad/sec. But now i assume because the amount of force is reliant on the time (in other words, is accelerating at a non-constant rate), some integration will be needed. The problem for me is, i have only the vaguest idea of how to actually integrate. Would anyone mind helping me with this problem if it does in fact require integration, by showing me the exact steps? And if that is not the case, perhaps point me in the right direction?
You are correct. You will need to do an integral to determine the angular velocity.

You have already evaluated the a(t) at 10 sec to determine a|10 from

|a(t)| = |r|*|F(t)|/I = 140*|.5*t + .3*t2|

Since a(t) = dω/dt

then ω|10 = ∫a(t)*dt

or

ω|10 = 140*∫(.5t+.3t2)*dt = 140*(.25*t2 +.1*t3 + c) evaluated from 0 to 10.

Since you are told it was at rest at t=0, then the constant of integration c = 0.
 
  • #3
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Awesome, thank you for the walkthrough, that was incredibly helpful
 

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