This is another brief one to get you up to speed for the exam next week. This homework is due on Friday 11/9 at 4 pm.
First, two shear and moment problems: Prob. 7-77, 7-82
(Use the 5 steps…82 is the hardest one yet, so just take your time…)
Then, two cable problems: Prob. 7-94, 7-96
Note that cables as we have studied in Chapter 7 will NOT be on Exam 2, but shear and moment WILL FOR SURE be on the exam.
As usual, use this post as an open thread for discussion.
20 responses so far ↓
1 tpadden // Nov 7, 2007 at 9:52 pm
On problem 7-82, how do you deal with the segment pins connecting the structure at points B and E? What forces will they add to the structure and what moments, if any do they add?
2 hambut // Nov 7, 2007 at 10:29 pm
dude i think your looking at the wrong problem…
3 hambut // Nov 7, 2007 at 11:54 pm
anyone know if the 2000 lb force in 82 is added onto the load or is it just 2000 lb all together?
4 Alessandro // Nov 8, 2007 at 12:12 am
I believe it is a separate applied load, meaning you have the distributive loading and ontop of that you have 2000lb. If you do 500(9) + (0.5*500*9) you get something way bigger than 2000lb so I would think it is another external applied force. Any other ideas?
5 kls2ycc // Nov 8, 2007 at 12:35 am
for 82, on the graphing part, did you get a discontinuity at the 2000 point force for both the V and M graph? Also, did you get really large numbers?
6 Alessandro // Nov 8, 2007 at 12:53 am
Yeap, I’m getting big numbers, in the order of 5 digits.
7 kls2ycc // Nov 8, 2007 at 1:09 am
actually, i realized i messed up my moment equation, but when i went back it wasn’t discontinuous on the moment graph, however, I wasn’t sure if the moment at B is supposed to equal zero… because I got about 13500 for the moment at the end of the graph
8 Alessandro // Nov 8, 2007 at 1:16 am
The graph for the force is discontinuous at x= 9, but yea the moment graph is continuous. I did get zero at the end however when I plugged in x=18. I don’t think the moment at the end has a non zero value. (I might be wrong)
9 tpadden // Nov 8, 2007 at 10:12 am
sorry about that for some reason i was looking at 7-80
10 jmwakey7145 // Nov 8, 2007 at 3:17 pm
for 7-82 i made two method of section cuts. one before the 2000lb force and one after. Im having trouble with the moment equation for the cut after the 2000lb load. I don’t know how to model the resultant force of the distributed load when its a weird shape. like a trapezoid. anyone have any suggestions?
11 rsa8q // Nov 8, 2007 at 3:45 pm
alessandro, i agree that there should be no moment at point b in 7-82.
wakey, i would suggest using an integral to represent the force and moment for the distributed load.
12 kls2ycc // Nov 8, 2007 at 4:30 pm
for 7-82, i would suggest looking at example 7.8 on page 357. It was very helpful for me, and made a lot of sense, and helped me work the problem out without having to use integrals.
13 kls2ycc // Nov 8, 2007 at 4:32 pm
for problem 7-96, is the tension from B to the pulley the same as the force hanging from the pulley (15lb) ?
14 katie // Nov 8, 2007 at 4:59 pm
thats what i used as the tension..and i got 11.6 as x. anyone else? the answer isnt in the back.
15 katie // Nov 8, 2007 at 5:03 pm
ah and i also got 8.7, if i change one sign.
16 tpadden // Nov 8, 2007 at 5:21 pm
I am also lost on the second cut for 7-82…I don’t understand how to model a trapezoids centroid for the moment equation
17 rsa8q // Nov 8, 2007 at 9:57 pm
if anyone would like to check the answer to 7-96, i got xb = 5.65 ft
18 Vfort // Nov 8, 2007 at 10:16 pm
I got 5.65 ft as well….I cant get the trapezoid’s center of mass either…anyone??
19 tpadden // Nov 9, 2007 at 12:48 am
ok mclovin and I finally figured out how to do 7-82. The only way we could do this problem was making two cuts, one before the point load and one after the point load, and then working from B towards A so that we cut out having to use a trapezoid. Be sure to sum the moments around B and everything should work.
20 jmwakey7145 // Nov 9, 2007 at 8:50 am
thanks tpadden, i never thought to do it that way, but its much easier
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