Stuck in another static equilibrium problem

  • #1
Femme_physics
Gold Member
2,550
1

Homework Statement



At what distance "d", from point "A", the board with the person will slide whereas

http://img267.imageshack.us/img267/6139/skkkkkkk.jpg [Broken]

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Homework Equations



Weight of board = 50 [kg]
Weight of person = 100[kg]
Frictional coefficient between board and pit: Us = 0.4

c = 3[m] b = 4[m] a =10[m]


((The answer is d = 6.47 [m] ))


The Attempt at a Solution



I found all the unknowns, but I don't know how to answer the actual question. They're asking for the distance where the plank would slide with the person...can't see how I find that out....

http://img341.imageshack.us/img341/6096/zzzzaf.jpg [Broken]

Uploaded with ImageShack.us
 
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Answers and Replies

  • #2
nvn
Science Advisor
Homework Helper
2,128
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Dory: Excellent work, so far. (1) In your summation(Fx) equation, you used the wrong angles inside your two cosine functions. Check that, and correct that equation. (2) In your summation(MA) equation, you forgot to multiply your last two terms by the moment arm (distance) to those two forces. Correct that mistake.

Make the above corrections, and try again. By the way, please do not post wide images directly to the forum page. Just post a text link to wide images.
 
  • #3
Femme_physics
Gold Member
2,550
1
Ah...so it all comes down to silly miscalculations? I'm glad my method was correct :)

Sorry about the wide images... I got 1600 widescreen so I tend the think the world sees the web like I do :oops:

Many many thanks... I'll work on it!
 
  • #4
Femme_physics
Gold Member
2,550
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Got it! :D
 
  • #5
nvn
Science Advisor
Homework Helper
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Dory: Excellent work. One thing I forgot to mention is, the angle is 36.87 deg, instead of 36.86 deg. But luckily, this did not change the answer.

By the way, always leave a space between a numeric value and its following unit symbol. E.g., 100 [kg], not 100[kg]. See the international standard for writing units (ISO 31-0).
 
  • #6
Femme_physics
Gold Member
2,550
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Dooly noted... :) thanks
 

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