Solving 2D moments about point O

  • Thread starter Thread starter majunee
  • Start date Start date
  • Tags Tags
    2d Moments Point
Click For Summary

Discussion Overview

The discussion revolves around solving problems related to 2D moments about a point O, specifically focusing on calculating the magnitude of a force given a moment and determining an angle for a specified moment. The scope includes mathematical reasoning and conceptual clarification related to mechanics.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant presents a problem involving calculating the magnitude of a force based on a given moment and angle.
  • Another participant suggests completing a diagram to find the perpendicular distance from point O to the line of force.
  • A participant expresses uncertainty about their equation setup for the moment calculation.
  • Further hints are provided to draw additional lines and measure perpendicular distances to assist in solving the problem.
  • Some participants discuss the necessity of measuring distances perpendicular to the line of force rather than along the y-axis.
  • There is confusion regarding the variables used in the equations, particularly the meaning of "x" in one participant's equation.

Areas of Agreement / Disagreement

Participants generally agree on the need to measure distances perpendicular to the line of force, but there is disagreement and confusion regarding the setup of equations and the interpretation of the diagram.

Contextual Notes

Participants have not reached a consensus on the correct approach to setting up the equations, and there are unresolved questions about the diagram and variable definitions.

majunee
Messages
5
Reaction score
0
(a) The moment the force, F, makes about O is 15 N-m clockwise, and θ = 30˚, find the magnitude of F.
(b) If the force F = 100 N, determine the angle θ so the force develops a clockwise moment about point O
of 20 N-m. Limit your answers to a range of 0º ≤ θ ≤ 90º.

I'm a little lost can someone please help me with how to set up equations so i can figure out the answers. Thanx
 

Attachments

  • egr q.jpg
    egr q.jpg
    9.6 KB · Views: 1,281
Physics news on Phys.org
welcome to pf!

hi majunee! welcome to pf! :smile:

start by completing the diagram

continue the line of force backwards, and find its perpendicular distance from O :wink:
 
thanx so is this correct so far
-15 KN-m = F[-(sin30°)-(50mm)-(300sin60°)]
 
hmm … you're going to need another hint:

call that corner "C"

draw the line G through C parallel to F

draw the two perpendicular lines from O to G and from C to F …

how long are they? :wink:
 
Sorry I am really having trouble understanding the concept...
wouldnt 0-G be 300sin60 and c-f be 50 + xsin30
 
ahhh, you seem to be measuring vertical distances

no, to find the moment of a force, you need to measure distance(s) perpendicular to the line of the force :wink:

start again :smile:
 
how? if force has continuing line of action shouldn't we measure along the yaxis which would be like i did?
 
why the y axis? :confused:

(are we using the same diagram? … the force is at 30°)
 
yes we are
so would it be -300sin60 + 300 cos 60 - 50 + xsin30 - x cos 30
 
  • #10
why the y axis? :confused:

and what is the "x" in your equation?
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
4K
  • · Replies 6 ·
Replies
6
Views
8K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 24 ·
Replies
24
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K