# Engineering Statics Question

• andrew.c
In summary, the conversation is about a question involving resolving forces into components and using the equation M = Fd. The person provides their attempt at solving the problem, which involves calculating the moments created by the individual elements of R. They also mention getting stuck and asking for help. The expert gives advice and points out a mistake in the person's calculation, which leads to them getting the correct answer.

## Homework Statement

http://img512.imageshack.us/img512/2617/staticsquestion4.jpg [Broken]

## Homework Equations

- Ability to resolve forces into components
- M = Fd

## The Attempt at a Solution

(a)
Resolve the force acting at an angle into components...
10kN force = -10cos50i - 10 sin 50 j kN

Therefore, resultant R becomes...

= (-10cos50)i + (15 - 3 - 10 sin 50)j kN
= -6.428i + 4.3396j kN

(with a magnitude of 7.756kN)

(b) This is where I get stuck.

I basically calculated the moments created by the individual elements of R,

F1 = 15kn force
F2 = 3kn force
F3 = vertical component 10kn force
and, because I am using the joint with the wall as an origin, the line of action of the horizontal component passes through my origin thus no moment.

M1 = 15*3 = 45kNm
M2 = -3*1.5 = -4.5kNm
M3 = (-10 sin 50)*9 = -68.944kNm

Sum of moments = 45 - 4.5 - 68.944 = -28.444kNm

and then I get stuck. Do you add the moment you've just found to the moment provide in the couple, then sub. back into M=Fd where F=R?

Help!

Last edited by a moderator:
andrew.c: Nice work. The answer to the question in your last paragraph is yes. Also, notice a mistake in your M2 equation.

nvn said:
Also, notice a mistake in your M2 equation.

Yes, should use 4.5, not 1.5.
Thanks, I got the right answer!