# Statics - Moments

#### ZaZu

1. Homework Statement

I got a problem solving this question.

http://img228.imageshack.us/img228/7049/image164.jpg [Broken]

3. The Attempt at a Solution

Im not sure if im missing a rule here. I take CW to be positive and CCW to be negative.
But my attempt to solve it failed =[

http://img220.imageshack.us/img220/7638/image165.jpg [Broken]

Your help is really appreciated :)

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#### PhanthomJay

Homework Helper
Gold Member
Looks like you forgot to multiply by the moment arm perpendicular distance to the pivot. Also, check your signs for each of the torques.

#### ZaZu

Looks like you forgot to multiply by the moment arm perpendicular distance to the pivot. Also, check your signs for each of the torques.
Yes, the distance x, correct ?? Its M= F . x .. But how can I find x ? :S

#### PhanthomJay

Homework Helper
Gold Member
A torque of a force or force components is calculated by multiplying the force or force components times the perpendicular distance between the line of action of that force and the pivot. You alreadty I think have the vertical component of each force. So what's the perpendicular distance, and what are the signs of the torques?

#### ZaZu

The first force is acting at a clockwise direction, it is positive.
The second force is acting at an anti-clockwise direction, it is negative.

Regarding the Perp. distance, its just not clicking in my head.

#### ZaZu

Ok wait, do you mean by perp. distance is the distance given between the pivot and the force itself ?? Which is 3x10^-3 for F1 and 3.8x10^-3 for F2 ?

#### PhanthomJay

Homework Helper
Gold Member
No, you are looking for the torque of both forces about the NUT. They both seem ccw, no? Also, regarding perpendicular distance from the horizontal force components to the nut, they are ___ and ___ for each horizontal force component?

#### ZaZu

Ok I think i got it :D :D

http://img80.imageshack.us/img80/2008/image167k.jpg [Broken]

Im not sure about the final result though, is it N or Kn or Nm ..
The given answer is 81.1N .. I found 8116 .. hmm if the supposed answer is 81.1Kn then my answer would be correct for N.

Correct me if im mistaken.

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#### PhanthomJay

Homework Helper
Gold Member
Ok I think i got it :D :D

http://img80.imageshack.us/img80/2008/image167k.jpg [Broken]

Im not sure about the final result though, is it N or Kn or Nm ..
The given answer is 81.1N .. I found 8116 .. hmm if the supposed answer is 81.1Kn then my answer would be correct for N.

Correct me if im mistaken.
Watch your units. If the torque is in N.m, then Force should be in Newtons and distance should be expressed in meters.

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#### ZaZu

Watch your units. If the torque is in N.m, then Force should be in Newtons and distance should be expressed in meters.
So where does that leave me ?? Am I supposed to convert or anything ?? If I divide by 100 I get the correct answer. But I want to know why am I dividing by a hundred.

Can you please tell me ? I got test tomorrow and its getting late =\
I really need to know how to correct my mistakes !

Bump =\

#### PhanthomJay

Homework Helper
Gold Member
So where does that leave me ?? Am I supposed to convert or anything ?? If I divide by 100 I get the correct answer. But I want to know why am I dividing by a hundred.

Can you please tell me ? I got test tomorrow and its getting late =\
I really need to know how to correct my mistakes !
Fsin60(.3m) + Fsin70(.38m) = 50N.m
F= 80.1N

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