Help in finding the magnitude of a force

  • Thread starter tmn50
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  • #26
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I am trying but I'm having difficulty getting through to you.
Read all three of newtons laws
http://en.wikipedia.org/wiki/Newton's_laws_of_motion
What I am saying is a combination of all three of them. Let me just think a little more about to break it down so you see how each one applies in this case.
 
  • #27
Delphi51
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I wouldn't say that how can a skater's feet stand such a force this sport would have been banned if it was so
Have you calculated the force?
I think we agree there is a centripetal acceleration and force for the circular path up to the point C. If you accept the force a nanometer before C, why does it suddenly become so unreasonable to have it for one more infinitesimally small distance?
 
  • #28
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what about the first poin of the circular path is there any vertical acceleration ?
the body started with no speed
and I don't know there is something which make no sense in this when i calculated the force it was 2400 N (nothing wrong ) while mg = 800 N
 
  • #29
Delphi51
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At the top of the circular path, velocity = 0 so no centripetal acceleration.
The skater does accelerate downward as if in free fall. However, a nm down the path there is some velocity and a tiny bit of centripetal acceleration to the left. As the skater continues to fall, velocity and centripetal acceleration increase.

Your 2400 N calc is for centripetal force plus gravitational force, right?
I'm finding it interesting that the centripetal force is twice the gravitational force regardless of the height = radius. Since potential energy is converted entirely to kinetic energy as it falls,
PE at top = KE at bottom
mgR = ½mv²
v² = 2gR
Putting this into Fc = mv²/R
gives Fc = 2mg.
The total force pushing up on the skater at the bottom of the path is three times gravity regardless of the radius. Most interesting! Skateboarders are experiencing 2 G's of acceleration but feeling 3 times their normal weight at the bottom of a bowl.
 
  • #30
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thanks man I really apreciate it:biggrin:
 
  • #31
Delphi51
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Most welcome. Quite an interesting problem, too.
 
  • #32
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thanks a lot Delphi51. I don't think would have managed to make it that clear.
 
  • #33
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