Solving Winch Puller Statics Homework: Find Tension at D

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Homework Help Overview

The problem involves determining the tension in a winch puller cable required to create a specific moment about point D to straighten a fence post. The context includes forces, moments, and angles related to static equilibrium.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relationship between torque, force, and distance, with some questioning the use of specific equations and the interpretation of moment arms. There is an exploration of how to correctly apply the concepts of moments and forces in this context.

Discussion Status

The discussion is ongoing, with participants providing insights into the calculations and the necessary components for determining the tension. Some guidance has been offered regarding the moment arm and the need for a perpendicular distance in torque calculations.

Contextual Notes

There are mentions of specific values and angles, as well as a reference to the need for clarity on the units used in calculations. Participants are also reflecting on the assumptions made regarding the forces acting on the system.

talaroue
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Homework Statement



It is known that a force with a moment of 960N*m about D is required to straighten the fence post CD. If d=2.8 (already replaced), determiethe tension that must be developed in the able of winch puller A o create the reuired moment point D.

Statics3.jpg


Homework Equations


W=Fd
Fx=Fcos(theata)


The Attempt at a Solution



Fx=TAB*sin(17.78)
Fy=TAB*cos(17.78)

MD=TAB*sin(17.78)

960=TAB*sin(17.78)*.898m
TAB=1122 N

Answer is:1224 N

but how?
 
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any ideas would be great!
 
You're looking for the torque, or moment-arm, about point D due to the rope tension. There should be a formula in your book to calculate this, it will involve force, distance, and an angle -- but it's not the equation for work that you quoted.
 
thats the equation for a moment about D
 
in my book it even stats that instead of putting the normal units for work I should put N*m.
 
talaroue said:
thats the equation for a moment about D
Yes, exactly. You need the moment arm, due to the cable, about D. In other words, the perpendicular distance from D to the cable.

talaroue said:
in my book it even stats that instead of putting the normal units for work I should put N*m.
That's right.
 
Statics3-Work.jpg


I got .898 because that is the height of the pole. Since the force for the x direction makes the system go counterclockwise it is positive. The force in the y direction is non exsistent because it goes along the line of action so if i push straight down on the pole it doesn't move. The angle at A is the same as the angle of the force. So why doesn't my work work?
 
Draw a line from D to the cable, perpendicular to the cable. That is the distance to use for calculating torque.
 

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