Problems 1 and 2. Locate the centroid of the shaded area y r = 100 mm x 50 mm -180 mm 1. 2. 100 mm 50 mm —200 mm 140 mm 140 mm X

International Edition---engineering Mechanics: Statics, 4th Edition
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ISBN:9781305501607
Author:Andrew Pytel And Jaan Kiusalaas
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Chapter8: Centroids And Distributed Loads
Section: Chapter Questions
Problem 8.7P: Using integration, locate the centroid of the area under the n-th order parabola in terms of b, h,...
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ENTROIDS AND CENTER OF GRAVITY: The following problems are to locate centroids of areas and lines. PROBLEM 2 ONLY PROVIDE THE SAME PROCESS OF SOLUTION IN THE GIVEN EXAMPLE ? THANK YOU.

Problems 1 and 2. Locate the centroid of the shaded area
r 100 mm
x
50 mm
-180 mm
1.
2.
100 mm
50 mm
-200 mm
140 mm
140 mm
X
Transcribed Image Text:Problems 1 and 2. Locate the centroid of the shaded area r 100 mm x 50 mm -180 mm 1. 2. 100 mm 50 mm -200 mm 140 mm 140 mm X
2. Locate the centroid of the shaded area shown.
Divide the area into regular geometric shapes. Make
sure the centroids of the geometric shapes can be
identified.
6″
a, in².
(1/2)(12)(6)=36
(12)(6)=72
|-(1/2) (12) (6)=-36
A=72
Part
Total
Σαχ
x =
A
x = 5"
Σαν
y =
A
y = 6"
=
360
72
432
72
12"
The area can be divided into three parts
as shown, with the unshaded triangle as
a negative area since it is not part of the
shaded area.
x, in
y, in
8
4
6
3
ax, in³
(36)(4)=144
(72)(6) = 432
(-36) (6)=-216
360
ay, in³
(36) (8)=288
(72)(3)=216
(-36) (2)-72
432
6
2
3. Locate the centroid of the shaded area in the figure,
created by cutting a semicircle of diameter r from a
quarter circle of radius r.
a, in².
x, in
y, in
Part
Quarter
circle
πr²
4r
ax, in³
πr²/4r
4r
3π
3π
4 3TT.
Semicircle
4r
πr (4rv
бл
2
8 6π
Total
3r-³
12
Σαχ
x =
A
x=0.636r
y =
y = 0.349r
TT (+)²
2
πr²
8
A =
0.25r³
0.393r²
ay_0.137³
= 0.393r²
πr²
8
= 0.393r-²
= 0.257-³
7.3
12
ay, in³
πr² 4r
4 3π
пре
8
0.13713
πr-3
16
4 mi
5. Locate the centroid of the built-up section shown in the figure. Refer to Table 6-6.2
on page 199 of your textbook for the properties of the elements.
8" x 6" x 1"
8" x 6" x 1"
16" x 1"
5" x 3" x 1/2"
5" x 3" x 1/2"
12"-20.7 lb channel
Solution:
Since the cross section is symmetrical with respect to a vertical axis, the centroid of the
cross section lies on the axis of symmetry. Therefore, only the location of the centroid with
respect to a horizontal axis will be determined.
With the base of the cross section as the reference:
8" x 6" x 1"
8" x 6" x 1"
16" x 1"
5" x 3" x 1/2"
5" x 3" x 1/2"
Part
2-8"x6"x1"
16" x 1"
2-5"x3"x1/2"
12"-20.7 lb channel
a, in².
2(13)=26
(16)(1)=16
2(3.75)=7.5
6.03
A=55.53
Σαγ
Total
524.806
55.53
y =
A
y = 9.45" above the base of the cross section
LOTININ
12"-20.7 lb channel
RSITY
DIFINAL
y, in
16.28 -1.65 14.63
8 +0.28 8.28
0.75 +0.28 = 1.03
0.70
16" +0.28" 16.28"
ay, in³
380.38
132.48
7.725
4.221
524.806
Transcribed Image Text:2. Locate the centroid of the shaded area shown. Divide the area into regular geometric shapes. Make sure the centroids of the geometric shapes can be identified. 6″ a, in². (1/2)(12)(6)=36 (12)(6)=72 |-(1/2) (12) (6)=-36 A=72 Part Total Σαχ x = A x = 5" Σαν y = A y = 6" = 360 72 432 72 12" The area can be divided into three parts as shown, with the unshaded triangle as a negative area since it is not part of the shaded area. x, in y, in 8 4 6 3 ax, in³ (36)(4)=144 (72)(6) = 432 (-36) (6)=-216 360 ay, in³ (36) (8)=288 (72)(3)=216 (-36) (2)-72 432 6 2 3. Locate the centroid of the shaded area in the figure, created by cutting a semicircle of diameter r from a quarter circle of radius r. a, in². x, in y, in Part Quarter circle πr² 4r ax, in³ πr²/4r 4r 3π 3π 4 3TT. Semicircle 4r πr (4rv бл 2 8 6π Total 3r-³ 12 Σαχ x = A x=0.636r y = y = 0.349r TT (+)² 2 πr² 8 A = 0.25r³ 0.393r² ay_0.137³ = 0.393r² πr² 8 = 0.393r-² = 0.257-³ 7.3 12 ay, in³ πr² 4r 4 3π пре 8 0.13713 πr-3 16 4 mi 5. Locate the centroid of the built-up section shown in the figure. Refer to Table 6-6.2 on page 199 of your textbook for the properties of the elements. 8" x 6" x 1" 8" x 6" x 1" 16" x 1" 5" x 3" x 1/2" 5" x 3" x 1/2" 12"-20.7 lb channel Solution: Since the cross section is symmetrical with respect to a vertical axis, the centroid of the cross section lies on the axis of symmetry. Therefore, only the location of the centroid with respect to a horizontal axis will be determined. With the base of the cross section as the reference: 8" x 6" x 1" 8" x 6" x 1" 16" x 1" 5" x 3" x 1/2" 5" x 3" x 1/2" Part 2-8"x6"x1" 16" x 1" 2-5"x3"x1/2" 12"-20.7 lb channel a, in². 2(13)=26 (16)(1)=16 2(3.75)=7.5 6.03 A=55.53 Σαγ Total 524.806 55.53 y = A y = 9.45" above the base of the cross section LOTININ 12"-20.7 lb channel RSITY DIFINAL y, in 16.28 -1.65 14.63 8 +0.28 8.28 0.75 +0.28 = 1.03 0.70 16" +0.28" 16.28" ay, in³ 380.38 132.48 7.725 4.221 524.806
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