Winch puller tension for 960 N·m moment at point D

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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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Discussion

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.
 
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.