Rotation Problem

  • Thread starter KTiaam
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  • #1
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Homework Statement



A coin is spinning on its edge at 5 rotations per second.
Friction slows down its spin rate at .4 r/s2

a) what angular displacement does the coin have by the time it's slowed down to half its original angular velocity.

b) how long before the coin stops spinning?
 

Answers and Replies

  • #2
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5 rev per second = 10 pi radians per second

[itex]\alpha[/itex] = 0.4 r/s2
ωi (angular velocity initial) = 10 pi r/s
ωf (angular velocity final) = 5 pi r/s

Δθ = angular displacement

Known equations

ωf2 = ωi2 + 2[itex]\alpha[/itex](Δθ)

I tried plugging the know variables in but i keep getting a negative answer.

btw answer is supposed to be 924 Rad.
 
  • #3
haruspex
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5 rev per second = 10 pi radians per second

[itex]\alpha[/itex] = 0.4 r/s2
Is it getting faster or slower?
 
  • #4
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Is it getting faster or slower?
slower. that does not make velocity negative though?
 
  • #5
haruspex
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It'll make alpha negative.
 

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