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Homework Help: Static Friction Force

  1. Nov 21, 2006 #1
    Car 1 with mass m rounds a curve of radius R traveling at a constant speed v. Car 2 with a mass 2m rounds a curve of radius 2R at a constant speed 2v. How does the magnitude F2 of the sideward static friction force acting on car 2 compare with the magnitude F1 of the sideward static friction force acting on car 1?

    a. F1 = 4F2
    b. F1 = 2F2
    c. F1 = F2
    d. F2 = 2F1
    e. F2 = 4F1
     
  2. jcsd
  3. Nov 21, 2006 #2

    radou

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    In order to get some help, you should show some efforts first.
     
  4. Nov 21, 2006 #3
    sorry, I had listed my knowns but it didn't show

    Anyways

    I know that car 1 has half of everything car 2 has, so wouldn't it make sense that F2 = 2F1?
     
  5. Nov 21, 2006 #4

    radou

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    Hint: compare the centripetal forces.
     
  6. Nov 21, 2006 #5
    Ok the equation of centripetal forces is mv^2/r. The force of car one is simply mv^2/r and the centripteal force of car 2 would be 4mv^2/2r which equals 2mv^2/r. So Force of car 2 is twice that of force of car 1 so F1=2F2?
     
  7. Nov 21, 2006 #6

    radou

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    The centripetal force exerted on the second car is 2m (2v)^2/(2R) = 4m v^2/R.
     
  8. Nov 21, 2006 #7
    what happened to 2R?
     
  9. Nov 21, 2006 #8

    radou

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    [tex]2m \frac{(2v)^2}{2R}= 2m \frac{4v^2}{2R}= 2m \frac{2v^2}{R}= 4m \frac{v^2}{R}[/tex]. I hope you agree on that. :smile:
     
  10. Nov 21, 2006 #9
    ok ok i see what you did now
     
  11. Nov 21, 2006 #10
    so then that means F2 = 4F1
     
  12. Nov 21, 2006 #11

    radou

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    Yes, since the sideward frictional force should balance the centripetal force.
     
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