Statics problem- with solutions but have question about the moment

Jan 2011
Hello everyone, i nearly finished the problem but I get the wrong moment, so i would like to know what I missed. See the image in the attachment.

So the questions is as a following: Replace all the 4 forces and the moment in the figure with a resultant R and a resulting moment M in Point 0. Also give direction of R in comparison to the x axis.

The correct answers should be R = 148,3 N, Angle = 63,2 and Moment : -273,3 N

I will now present my solution:

Rx = 40-60cos45 + 80 cos30 = 66,8556
Ry = 50+60sin45+80sin30 = 132,426

R = SQRT((66,8556^2)+(132,426^2)) = 148,345

tan alpha = O/A = 132,426/66,8556 = 63,213 after using inverse of tan.

Now to my problem where I am stuck Is calculating the moments ok lets do it

Mo (with right hand rule) : 140-50*5-42,464*7+42,4264*4=
140-250-296,985+169,706 = - 237,279

This is where I need your help. What did I do wrong? Did i miss something?

Could someone tell me and show me analytically how it should be solved?

Thank you.



PHF Helper
Jun 2010
Morristown, NJ USA
I get the same answers as you. I suspect that your text book has a typo in the answer for the moment, i.e. should be -237.3 N-m.
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