Question

can some body please check out my solution to the problem here (just point out the mistakes )

Answer 1

this is the original question with answer (from the solution manual of the book)
http://puu.sh/nmc9L.png

Answer 2

this is a general book example http://puu.sh/nmd5h.png

Answer 3

here you can see my solution (done in the logical manner ) http://puu.sh/nmedP.jpg

Answer 4

which one is correct

Answer 5

I agree with your answer.

If you put the force (F) and lever arm (r) vectors tail to tail, you'll find that the angle between them is 120°. This is the angle that should be used in the equation to determine torque. I think this is a case where the book made a mistake (although I noticed the question says 5N even though the diagram shows 10N).