TRUSS QUESTION URGENTTTT!!! how to do Q12 b) of 2004 hsc paper (1 Viewer)

[tryin2study]

this question is of the 2004 hsc paper . Question 12b) i need 2 noe the reaction in Support 1 and the magnitude and nature of force of member A
THIS IS URGENTTTTTTTT SOO ASPAPP
wit the working wuld be helpful

 

[cwag]

the trick in this question is to take the centre of mass (4kN) at the centre of the truss (seeing as its symmetrically loaded). therefore to find reaction at support 1 we take moments about support 2.

Sum of all moments about support 2 = 0 (i will take clockwise rotation as being +)

therefore; 190 * 3 - 2*4000 - 7*450 + 4*(support 1) =0
............support 1 = 10580/4
=2645N

now..to find force in member a, i will do method of sections...taking the section diagonally up through the second member from the left on the top of the truss..and the sum of all the moments about the point directly above member a = 0......therefore taking clockwise rotation as positive we get

0= - 450*2+ A*root3 (simple trig, exact angle triangle)
A= 519.6N (force is towards joint so member is in compression)


sorry its kind of hard to explain without diagrams.

 

[MoNNiE]

the trick in this question is to take the centre of mass (4kN) at the centre of the truss (seeing as its symmetrically loaded). therefore to find reaction at support 1 we take moments about support 2.

Sum of all moments about support 2 = 0 (i will take clockwise rotation as being +)

therefore; 190 * 3 - 2*4000 - 7*450 + 4*(support 1) =0
............support 1 = 10580/4
=2645N

now..to find force in member a, i will do method of sections...taking the section diagonally up through the second member from the left on the top of the truss..and the sum of all the moments about the point directly above member a = 0......therefore taking clockwise rotation as positive we get

0= - 450*2+ A*root3 (simple trig, exact angle triangle)
A= 519.6N (force is towards joint so member is in compression)


sorry its kind of hard to explain without diagrams.

see the following post for the solution to your question
http://community.boredofstudies.org/showpost.php?p=2574239&postcount=11


i did a solution for this awhile ago, along with a few others

best wishes