Statics: Solving Moments Homework Help

In summary, the conversation is about solving a problem involving the calculation of torque. The person asking for help forgot to multiply by the perpendicular distance to the pivot and was unsure about the signs of the torques. After some discussion, they were able to correctly calculate the torque to be 50 N.m, but had trouble with the units and had to divide their answer by 100 to get the correct value of 81.1 N.
  • #1
ZaZu
36
0

Homework Statement



I got a problem solving this question.

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

The Attempt at a Solution



Im not sure if I am 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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  • #2
Looks like you forgot to multiply by the moment arm perpendicular distance to the pivot. Also, check your signs for each of the torques.
 
  • #3
PhanthomJay said:
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
 
  • #4
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?
 
  • #5
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.
 
  • #6
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 ?
 
  • #7
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?
 
  • #8
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 I am mistaken.
 
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  • #9
ZaZu said:
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 I am mistaken.
Watch your units. If the torque is in N.m, then Force should be in Newtons and distance should be expressed in meters.
 
Last edited by a moderator:
  • #10
PhanthomJay said:
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 !
 
  • #11
Bump =\
 
  • #12
ZaZu said:
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 !
It must be your algebra:
Fsin60(.3m) + Fsin70(.38m) = 50N.m
F= 80.1N
 

What is statics?

Statics is a branch of mechanics that deals with the study of objects at rest or in constant motion. It focuses on the balance of forces and moments acting on an object, and how these forces affect the object's stability and motion.

What are moments in statics?

Moments, also known as torque, are a measure of the tendency of a force to cause an object to rotate around an axis. In statics, moments are calculated by multiplying the force by the perpendicular distance from the axis of rotation.

How do I solve moments in statics?

To solve moments in statics, you need to first identify all the forces acting on the object and their respective distances from the axis of rotation. Then, you can use the equation M = Fd to calculate the moment, where M is the moment, F is the force, and d is the distance from the axis of rotation.

What are the common methods for solving moments in statics?

The most commonly used methods for solving moments in statics are the graphical method, the analytical method, and the moment of inertia method. The graphical method involves drawing a free-body diagram and using geometric principles to solve for the unknown moments. The analytical method uses mathematical equations to calculate the moments, while the moment of inertia method involves calculating the moments based on the object's shape and mass distribution.

Why is statics important?

Statics is important in many fields of engineering and science as it provides a foundation for understanding the behavior of objects under various forces. It is essential for designing structures and machines that are safe, stable, and efficient. It also helps in the analysis and prediction of the behavior of structures and machines, which is crucial for their proper functioning.

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