How to calculate moments to find a force

[Sully1071]

I'm looking at a problem and am having trouble finding the force using moments. To be honest I'm not sure am i going about it the correct way.

Attached is a sketch of the problem,

Is the cclockwise moment about A = .5m(1000N) = 500Nm
and the anti clockwise moment about A = .75m(F)

can these be equated to find F??

Thanks

 

[zoobyshoe]

Your image is too tiny.

 

[Sully1071]

Sorry, attached is a bigger image in a word document.

 

[tiny-tim]

Welcome to PF!

Hi Sully1071! Welcome to PF!

Is the cclockwise moment about A = .5m(1000N) = 500Nm
and the anti clockwise moment about A = .75m(F)

can these be equated to find F??

Yes, that's exactly correct …

(except that you've mixed up clockwise and anti-clcokwise! )

and yes, you now equate the clockwise to the anti-clockwise.

Why is that worrying you? ​

 

[Sully1071]

Im just unfamiliar with unfamiliar with these calculations but have to do them as part of a project.

If i use the new free body diagram attached and the unit was to rotate about point a i assume my new moments would be calculated by:

Anticlockwise moments = 1000(.65)
Clockwise moments = F(.6)

 

[tiny-tim]

Hi Sully1071!

Is this a new problem? …

sorry, I'm on an iMac, and it won't show images in .doc

(but I could see your original .jpg)

 

[Sully1071]

jpeg is attached

 

[tiny-tim]

ah! nice and big!

If i use the new free body diagram attached and the unit was to rotate about point a i assume my new moments would be calculated by:

Anticlockwise moments = 1000(.65)
Clockwise moments = F(.6)

yes that's right

generally, the moment of a force F is the dot product F.d,

which you can do as either F times the perpendicular distance (your method)

or as F times the whole distance times sine of the angle between ​