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 Post subject: rotational kinematics
PostPosted: Tue, 25 Mar 2008 04:05:30 UTC 
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At a grinding wheel has an angular velocity of 30.0 rad/s . It has a constant angular acceleration of 27.0rad/s^2 until a circuit breaker trips at time = 2.30 . From then on, it turns through an angle 436 rad as it coasts to a stop at constant angular acceleration.

Through what total angle did the wheel turn between and the time it stopped?

I got theta=576 rad, which is correct

At what time did it stop?

I used t=2(theta_f-thea_i)/w_0+w_f, where w_f=w_0+(alpha)t

so t=(2*436)/(30+92.1)=7.14 But this is wrong. Where did I err?

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PostPosted: Wed, 26 Mar 2008 04:44:43 UTC 
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You used the wrong values for \omega_i and \omega_f. The initial velocity is 92.1 rad/s and the final velocity is zero. Also, don't forget to add the initial 2.30 seconds.


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