Can Someone Explain Statics and Torque for an Applied Maths Exam?

[Mutant_Fruit]

Hopefully someone here knows what I'm talking about, but here it goes.

I'm doing my leaving cert applied maths paper in 2 days time, and I'm stuck on this question. I can't follow the solution available on the internet, so i need someone to go through it step by step. Its Q7 in the paper here: http://www.examinations.ie/archive/exampapers/2001/LC020ALP1EV.pdf

Basically i drew up my diagram, marked in all the correct forces, balanced them horizontally and vertically, then split the rods up, and worked out the forces on each rod separately. (Should i have done that?).

Then i took moments on each rod, and tried solving between all my equations, but i couldn't get it to work out. The online solution is here: http://www.examinations.ie/archive/markingschemes/2001/LC020ALP1EV.pdf

Any help appreciated.

 

[Gokul43201]

What part of the solution don't you understand ?

 

[Gokul43201]

...Basically i drew up my diagram, marked in all the correct forces, balanced them horizontally and vertically, then split the rods up, and worked out the forces on each rod separately. (Should i have done that?).

Which part are you referring to - a or b ?

It is okay to cosider the rods separately so long as you include the forces and moments that hold the rods together rigidly (if they are rigid), though I don't see how this would help. If you have a rigid body, treat it as one object.

 

[arildno]

Personally, I felt that the solution online used a very strange point to compute the torques about.
I would use the corner defined by the two rods.

 

[Mutant_Fruit]

I got it figured. My problem was that i was splitting the rods. I shouldn't have done that.

I decided just to take the basics of what the solution was telling me, which was to balance forces horizontally and vertically, and take moments about O, and it worked out perfectly.

I was complicating things hugely by splitting the rods, as i then probably would have needed 3 sets of moments (torque) to work it out.

 

[KnowledgeIsPower]

I got it figured. My problem was that i was splitting the rods. I shouldn't have done that.

I decided just to take the basics of what the solution was telling me, which was to balance forces horizontally and vertically, and take moments about O, and it worked out perfectly.

I was complicating things hugely by splitting the rods, as i then probably would have needed 3 sets of moments (torque) to work it out.

What do you mean by torque? I haven't encountered the expression before. Is that just another word for moments, or the forces you take into account when taking moments?

 

[HallsofIvy]

What do you mean by torque? I haven't encountered the expression before. Is that just another word for moments, or the forces you take into account when taking moments?

Torque is "the forces you take into account when taking moments" roughly speaking. More accurately, given a force applyed at point a, to find torque "about point b", draw the line segment from a to b, then multiply the component of the force perpendicular to the segment by the length of the segment. Notice that the same force will give different torques about different points.