phy201
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I have two question, the first I plan on taking test two on Monday 5/10/2010, and I know the final is due by the may 13, I was wondering if I could take it on friday may 14 instead or will that mess you up, I have had some issue were I am a little behind, I also intend to have all the lab work done by the weekend, so that it can be graded and I can submit any needed changes by Monday.
Thank You
Natalie
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The 14th is fine. Check with the Learning Lab to be sure of their hours.
phy201
Your 'question form' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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I forgot to ask my other question, I was reviewing for the test two and came across a test question that stumped me, It abnout the uniform sphere with a given mass with friction with a given torgue and then the disk with three masses and distance for each mass. It then askes us to find the KE of the spehere as it rotated through 5 radians using work/energy, since KE=1/2I omega^2, and omega= radian/sec, I am confused on how to convert this, do I need to find alpha first with the given torque and the Inertia that I calculatede and go from there. I work out all the queries for up to query 33 and I had no questions so I did not submit, i have looked them over but know I am confused.
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You would first find the moment of inertia I.
Then from the net torque you find the angular acceleration alpha.
Presumably the sphere starts from rest and accelerates through 5 radians.
You could use uniformly accelerated motion, though in this case the question specifies that you should use work-energy so you should use that method. However it's worth reviewing how you would use uniformly acceleration motion:
You know initial angular velocity, angular acceleration and angular displacement. If you know velocity, acceleration and displacement you can go to the fourth equation of unif. accel. motion to find final velocity. At this point you can find the KE. In some cases you need to go further with the analysis of the motion. Having found omega_f, you could then use initial and final angular velocity to find average angular velocity, which with displacement will give you the time interval. Or you could just solve the third equation of motion for the time interval. (Be sure to express the 3d and/or 4th equation in the symbols for angular motion, using alpha, omega, theta instead of a, v and `ds).
On this problem, though, you want to use the work-energy theorem, which in this case is also easier than the analysis of motion:
The work done by the net torque is equal to the net torque multiplied by the angular displacement: `dW_net = tau_net * `dTheta. This is completely analogous to `dW_net = F_net * `ds.
By the work-energy theorem `dW_net = `dKE.
You do have to be careful to use the net torque. The applied torque is given, but you have to also figure out the frictional torque, which will oppose the given torque.