 Physics Help Forum confusion about how to calculate rotations when given angular velocity
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 Periodic and Circular Motion Periodic and Circular Motion Physics Help Forum Mar 10th 2010, 01:33 PM #1 Junior Member   Join Date: Sep 2009 Posts: 9 confusion about how to calculate rotations when given angular velocity In an example problem the book gives 500 rev/min. It says to solve for the number of revolutions in 5.5s you need to use the formula w=w_o+ \alpha t Why can't one just convert the revolutions into radians/second and multiply that with 5.5s? kind of like x=vt that would be the way to do it by only looking at the units of the solution Last edited by man_in_motion; Mar 10th 2010 at 01:35 PM. Reason: removed latex b/c getting wiered latex error   Mar 10th 2010, 02:23 PM   #2
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 Originally Posted by man_in_motion In an example problem the book gives 500 rev/min. It says to solve for the number of revolutions in 5.5s you need to use the formula w=w_o+ \alpha t Why can't one just convert the revolutions into radians/second and multiply that with 5.5s? kind of like x=vt that would be the way to do it by only looking at the units of the solution Please post the whole problem. How can the book gives the result in rev/min if it asks a number?
It's hard to understand where you're having problem since as stated, the problem is incomprehensible. Maybe your method works only when the angular acceleration is null and wouldn't work in the case the rotating object has an increasing angular acceleration. Just to be sure, please post the full problem.
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Isaac
If the problem is too hard just let the Universe solve it.   Jul 27th 2010, 12:44 PM   #3
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Posts: 24 Originally Posted by man_in_motion In an example problem the book gives 500 rev/min. It says to solve for the number of revolutions in 5.5s you need to use the formula w=w_o+ \alpha t Why can't one just convert the revolutions into radians/second and multiply that with 5.5s? kind of like x=vt that would be the way to do it by only looking at the units of the solution It's an old topic, thus sorry for re-opening it Here's my attempt:

Converting 500 rev/min

= [500 X 2pi] / 60
= 52.4 radians / sec

Now Use the ratio method

1 sec = 52.4 rads
5.5 sec = x

x = 288.2 rads

Now to get your answer in rev/sec simply divide this by 2pi

= 288.2 rads / 2pi
= 45.9 revs / sec

I did whole working to make it easier for you. After you have grasped it, you can simply do the following

[500 revs / min] divided by 60

To get revs / sec

Now just multiply your answer by 5.5 secs Hope this helps!  Tags angular, calculate, confusion, rotations, velocity Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post SpeedBirdNine Kinematics and Dynamics 3 Sep 16th 2011 08:23 AM ohm Kinematics and Dynamics 34 Jul 9th 2010 07:32 PM Rosanella Waves and Sound 4 Feb 17th 2010 01:14 AM pauljholt Kinematics and Dynamics 4 Jul 4th 2009 10:04 PM asi123 Advanced Mechanics 0 Oct 22nd 2008 07:49 AM