ebook exercise

Dear all

I have the question related to the exercise explained in the book (chapter Forces, combination of noncurrent forces pg 41/668).

Can somebody explain to me how did you get the value of the distance for calculating the moment?
How did you get the value 4 mm and 6 mm?

Thank you

Dear Marina,
the distances can be taken considering the coordinates of the points of applications and of CR (numbers between paragraph).
For example let's take F2X. This is a force on X and the distance should be measured perpendicularly to the force, that is along the y axis (2nd coordianates). Coordinates (y) are 14 and 8, so the vertical distance from the force to cr is 6mm.
In the exercise book, you have usually a scale of 2:1, so just take a ruler , measure the distance and divide it by 2.

Thank you.
Now I have the question regarding exercise 6b in exercise book.

1. How do I know the distance from forces to CR without a ruler (taking into consideration the points that are provided - P1 and P2)
2. How do I calculate the moment for F1x ? (The F1 is vertical ,hence there is no X component, but on the other hand it's distant from CR - therefore it should provide a moment)

Thank you for your help

Distances can be found using the difference between coordinates. Since CR is (0,0) to facilitate the exercise, coordinates are also the distances from CR.
M = F*d, if F = 0 then M=0, no matter d.

Thank you for your answer.

Could somebody please write step by step solution to exercise 6c ?

I'm obviously wrong in calculating the M/F ratio....

I hope this image helps a bit (it is attached)!! I know my handwriting does not make things very easy. :silly: :silly:
So i went on and measured the distances as best as i could and the whole process goes from (1) finding the components of the forces (actually F2 is purely vertical) (2) Finding Fresultant in value and angle with inverse tangent (3) having measured the distance of the line of action of F1 = 20 mm we find 2 opposing monents of F1 and F2 and we find the resultant Moment. (4) the M/F ratio is 1125/156,5= 7,18 , which means the distance is approximately 7 mm from the CR and we just place the force accordingly to get the proper rotation. Hope this helped