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tmlrules
Joined: 26 Nov 2010 Posts: 2 Location: canada

Posted: Fri Nov 26, 2010 9:16 pm Post subject: Physics linear velocity to angular velocity, textbook wrong? 


Hi
Consider a race car that moves with a speed of 200mi/h. If it travels on circular race track of circumference 2.5 mi, what is the cars angular velocity?
First convert to meters/second and meters
Then the way I tried to solve was to find the raduis from the circumference.
c=(2pi)(r)
r=(c)/(2pi)
r=4023m/2pi
r=640m
Then
v=wr
w=v/r
w=89.4 m/s / 640m
w=0.139 rads/s which is angular velocity
But the textbook got 0.022 rads/s
they did w=v/r
but they used the full circumference 4023 meters
w=89.4 m/s / 4023m
w=0.022 rads/s
Why would they use the full circumference, when the raduis is supposed to be used? Thank you for answering, this is driving me crazy 

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hepcj Site Admin
Joined: 23 Jun 2007 Posts: 125

Posted: Sun Nov 28, 2010 12:24 pm Post subject: 


I think that it is a mistake in the book. It should be v = r w. How you have done the problem is correct. It is not uncommon for a few mistakes to find there way into the answers, but it should have been checked. 

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tmlrules
Joined: 26 Nov 2010 Posts: 2 Location: canada

Posted: Sun Nov 28, 2010 8:42 pm Post subject: Thanks 


Thank you very much . I got the same answer in two different ways, but I could not be sure if it was correct because of the answers in the back of the book. 

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