Static Friction of hollow sphere rolling up incline

  • #1
For hollow sphere rolling up incline:

I know that the kinetic friction will equal 2/3 acceleration since:

μgcosθ=2/3a

acceleration = 3/5gsinθ

so...kinetic friction = 2/5gsinθ

But how I do calculate the force of static friction??
 

Answers and Replies

  • #2
Would the static friction be the max static friction?
 
  • #3
Max static friction = tan θ times mgcosθ

Would the static friction exerted by incline on the hollow sphere be the max static friction?
 
  • #4
tiny-tim
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hi sweetpete28! :smile:
acceleration = 3/5gsinθ

so...kinetic friction = 2/5gsinθ

yes, the acceleration is 3/5gsinθ,

but there's no kinetic friction for a rolling object (beacuse there's no relative motion at the point of contact) …

that 3/5gsinθ is the static friction! :biggrin:
 
  • #5
Hi tiny-tim,

So the magnitude of the acceleration is equal to the force of the static friction??
 
  • #6
tiny-tim
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oops!

Hi tiny-tim,

So the magnitude of the acceleration is equal to the force of the static friction??

oops! :redface: i copied the wrong line! :rolleyes:

i meant that 2/5gsinθ :smile:
 
  • #7
But that is what I did and the answer is wrong:

For a I got 3.77 --> (3/5)gsin θ = (3/5)(9.81)(sin39.8degrees) = 3.77 (this is right)

Force of static friction = (2/5)gsinθ = (2/5)(9.81)(sin39.8degrees) = 2.51 (this is wrong)
 
  • #8
tiny-tim
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what about the mass?
 
  • #9
Mass of hollow sphere = 6.24kg but how does this factor in if:

μgcosθ = (2/3)a

solve for a: a = (3/5)gsinθ = 3.77 m/s^2

so Force of friction should = (2/3)(3.77) = 2.51 N....still dont understand why this is wrong...
 
  • #10
tiny-tim
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that's an acceleration!

multiply by the mass :wink:
 
  • #11
ok...

so Force of static friction = (m)(2/5)gsinθ = (6.24kg)(2/5)(9.81m/s^2)(sin39.8) = 15.7N...??

Right...?
 
  • #12
tiny-tim
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should be :smile:
 

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