Moments and the line of action of the resultant force

In summary, the student attempted to solve the homework equation but was not getting the correct answer. They figured out that the force acting at point A is 2.62 kN, which is not the result of a point load of 0.8N with distance 2.5m.
  • #1
nonyabus
7
0

Homework Statement



lrAVK.png


Homework Equations



ƩMoments = Moment + Fx*d + Fy*d

R = (Fx)i + (Fy)j

The Attempt at a Solution



I'm only interested in part (ii)

I calculated the components of the resultant force and they are

|R| = 1.15(i) + 9.36(j)

I know that the x-intercept of line of action is sum of moments divided by R(j) and y-intercept is sum of moments divided by R(i). I'm given a point A where the line of action goes through but I'm not quite sure how to use that bit of information to find M.

Any help is appreciated.
 
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  • #2
I have figured it out.

Since we know where the line of action acts, we must find the magnitude of the moment (M) that makes it act at that location. If we take moments about point A, then (M) is equivalent to the actions of the two forces about point A.

So I broke the two forces into their components, force × perpendicular distance... yadda yadda and I got the correct answer!
 
  • #3
f4Ho8.png


I don't know what this one is asking for, really... is it the resultant force on point A? Or the reaction force?

What I tried doing is represent the 2 kNm as 0.8N acting 2.5m away from A and normally calculate the moment by splitting the forces into components.

I'm not getting the right answer... here is my attempt:
R(i) = 3 cos 35

R(j) = -0.8 + 3 sin 35

|R|= 2.62 kN??
 
  • #4
Clues on the 2nd question, anyone?
 
  • #5
O.K. seems like I was wrong about the 2kN/m force. It can NOT be represented by a point load of 0.8N with distance 2.5m.

The magnitude of the force is the area of the triangle and where it acts is somewhere called the "centroid" (of a right triangle) and acts at two third's of its base.

http://www.ele.uri.edu/~daly/106/06/project/centroid/centroid.html
 

1. What is a moment in physics?

A moment in physics is a measure of the turning effect of a force on an object. It is calculated by multiplying the magnitude of the force by the perpendicular distance from the force to the pivot point.

2. How is the line of action of the resultant force determined?

The line of action of the resultant force is determined by finding the vector sum of all the individual forces acting on an object. This can be done using graphical or mathematical methods.

3. Why is it important to consider the line of action of the resultant force?

The line of action of the resultant force is important because it determines the direction in which an object will move or rotate. It also affects the stability and equilibrium of an object.

4. What is the difference between a moment and a force?

A force is a push or pull on an object, while a moment is a measure of the turning effect of that force. Forces cause linear motion, while moments cause rotational motion.

5. How does the distance from the pivot point affect the moment of a force?

The further away a force is from the pivot point, the greater the moment will be. This is because the longer the lever arm (distance from the pivot), the more torque the force can produce.

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