elica85 3 years ago find the centroid..drawing, one moment pls

1. elica85

|dw:1342574765308:dw|

2. elica85

y bar=(sum y local bar * area)/(sum area) so i thought it should be [(.5*1*5)+2(1*2*1)]/(1*5+2*1*2)... but solution says [(.5*1*5)+2(2*1*2)]/(1*5+2*1*2)

3. abstracted

What's the horizontal dimension across the top?

4. elica85

sorry, it's 5. so 3 on the smaller part

5. elica85

where they have "2", i have as 1 b/c...|dw:1342637555114:dw|

6. abstracted

Sorry for the wait, had to go do something + internet problems. for the two smaller portions it should be:\[2(1)2+2(1)2\]Which simplifies to\[2[2(1)2]\] You got the distance from the top to the center of the small triangle wrong, it should be 2 not 1. Note that they calculated the centroid from the top of the figure, not the bottom |dw:1342639178273:dw|

7. abstracted

And when i say triangle... I mean rectangle, ha

8. elica85

that explains everything since it's a problem of using shear formula so i have to find Q too which i was about to ask next. it all makes sense now but why is the centroid calculated from the top? is that the only way?

9. elica85

o, i believe you can. i was doing it wrong b/c when i got the y local bar for the top portion, i didn't use 2.5 if i were assuming the bottom to be centroid..klutz

10. abstracted

As far as the centroid calculation itself, It doesn't matter whether you calculate it from the bottom or top. If you calculated from the bottom you would get a different numerical answer, but it would still point to the centroid. I can't explicitly remember, but there may have instances where it is advantageous to calculate from the bottom or top

11. elica85

thank you!

12. abstracted

np!