Question

statics question !

Answer 1

i try summing the moments about point a but then i get confused when adding them up ): am i supposed to sum the moments about axis' instead?

Answer 2

RC Hibbeler right?

Answer 3

Simply the problem using a free body diagram, it would be much clearler then.
Yup, sum the forces and moments around axes.

Answer 4

yesss. okay so if i sum about the x axis, only d has a moment about it?

Answer 5

but it does not make sense because the sum of that moment should equal zero. but the moment of d about the x axis is 300lb x 6 ft which does not equal zero ?

Answer 6

i summed moments about the y axis and that works i think. only T and D have moment about it. so this should be good.

Answer 7

here is a little hint

Answer 8

fbd ! haha thanks. i am just wondering why there would not be a moment about the x axis?

Answer 9

i think there is moment around x axis.

Answer 10

and also i got an x value going the negative direction.

Answer 11

does T have moment about the x axis ?

Answer 12

yeah, methinks T has moment around all three axes.

Answer 13

ohhh because it does not intersect it.

Answer 14

okay so moment about x = T(2ft) - D(6ft) = 0
am i on the right trackkkk.

Answer 15

i am super confused. i dont think 2ft is the right distance.

Answer 16

yeah 2ft is not right there, this Tension needs to be broken down properly.

Answer 17

T= T(3/7)i - T(6/7)j + T(2/7)k
?

Answer 18

oh yeah! you got it now :) great.

Answer 19

yes but i have no clue what to do with that ^

Answer 20

now look at the FBD and formulate the moment equations, like for x it will be T 2/7 * distance - 300 * distance etc

Answer 21

um so make distance a variable?

Answer 22

can i make a position vector from each axis and do the cross product of that and T?

Answer 23

distance isnt variable, sorry, for that case its 6 ft.

Answer 24

ohhh. okay let me see.

Answer 25

I don't like this subject Engineering Physics, I won't take it when I go to college...

Can we use torques here? I am not sure but to use torques I will have to assume rods to massless and kind of not significant.

Answer 26

hold on, i am confused as to why the distance is 6 ft?

Answer 27

and yess, the subject is pretty brutal if you are not intuitive with direction senses but other than that, its pretty easy to crunch the numbers. and yes, i believe you can use torques because i think they are synonymous with "moments", which are what i am using.

Answer 28

..because i took moment at A, you free to use any other point, but see FBD.

Answer 29

you're

Answer 30

moment at A and not x axis?

Answer 31

@ishaan94 its engineering mechanics, yes you use torques, its equilibrium.
And its a compulsory subject.

Answer 32

i see that the distance between the x axis and B is 6 ft; shouldnt the moment arm be perpendicular to T?

Answer 33

Moment at A on the x axis perhaps.

Answer 34

There has to be a question like this, solved in the book. Give me a few minutes, i will get this thing worked out.

Answer 35

...only if you want to see the solution.

Answer 36

yes please (:

Answer 37

hmm what is the answer btw?

Answer 38

there is no answer in the book cause it is an even numbered problem haha.

Answer 39

I have no idea but do you think answer close to this acceptable?
http://www.wolframalpha.com/input/?i=300%2Farc+sin%281%2Fsqrt%2810%29%29

I didn't convert any unit to SI unit

Answer 40

Is this possible?