# Stuck in another static equilibrium problem

• Femme_physics
In summary, the question asks for the distance "d" from point "A" where the board with a person will slide. The weight of the board is 50 kg, weight of the person is 100 kg, and the coefficient of friction between the board and pit is 0.4. The distance is found to be d = 6.47 m. The correct angles were used in the summation(Fx) equation and the last two terms in the summation(MA) equation were multiplied by the moment arm. The angle is actually 36.87 degrees, but this did not affect the answer. It is important to leave a space between a numeric value and its unit symbol.

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## 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]

## 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]

Last edited by a moderator:
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.

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 Many many thanks... I'll work on it!

Got it! :D

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).

Dooly noted... :) thanks