Section 8.2 - Volumes by Slicing

7.3

Solids of Revolution

Find the volume of the solid generated by revolving the regionsabout the x-axis.2y x x and y 0 bounded by

12

0

r dx 1

22

0

dx xx

Find the volume of the solid generated by revolving the regionsabout the x-axis.2y 2sin2x, 0 x bounded by

/ 22

0

xr d

/ 2

2

0

dx2sin2x

Find the volume of the solid generated by revolving the regionsabout the y-axis.1

2y x, x 0, y 2 bounded by

22

0

r dy 2

2

0

d2y y

Find the volume of the solid generated by revolving the regionsabout the line y = -1.2y 3 x , y 1 bounded by

22

2

dxr

2

22

2

3 x 1 dx

The volume of the solid generated by revolving the first quadrantregion bounded by the curve and the lines x = ln 3 andy = 1 about the x-axis is closest to

x / 2y e

a) 2.79 b) 2.82 c) 2.85 d) 2.88 e) 2.91

ln3

2 2x / 2

0

e 1 dx

CALCULATOR REQUIRED

2

322

0

222

0

24 2

0

2 4

The volume of the solid generated by rotating about the x-axis

the region enclosed between the curve y 3x and the line

y 6x is given by

A. 6x 3x dx

B. 6x 3x dx

C. 9x 36x dx

D. 36x 9x d

2

0

22

0

x

E. 6x 3x dx

CALCULATOR REQUIRED

Let R be the region in the first quadrant above by the graph of

f x 2Arc tanx and below by the graph of y = x. What is the volume

of the solid generated when R is rotated about the x-axis?

A. 1.21

B. 2.28 C. 2.69 D. 6.66 E. 7.15

CALCULATOR REQUIRED

Let R be the region in the first quadrant that is enclosed by the

graph of f x ln x 1 , the x-axis and the line x = e. What is

the volume of the solid generated when R is rotated about the

line y = -1?

A.

5.037 B. 6.545 C. 10.073 D. 20.146 E. 28.686

CALCULATOR REQUIRED

e

2 2

0

ln x 1 1 1 dx 20.14627352 D Cross Sections

Let R be the region marked in the first quadrant enclosed bythe y-axis and the graphs of as shown in the figure below

2y 4 x and y 1 2sinx

R

a) Setup but do not evaluate the integral representing the volume of the solid generated when R is revolved around the x-axis.

b) Setup, but do not evaluate the integral representing the volume of the solid whose base is R and whose cross sections perpendicular to the x-axis are squares.

1.102

2 22

0

4 x 1 2sinx dx

1.102

22

0

4 x 1 2sinx dx

CALCULATOR REQUIRED

2 2

The region S is represented by the area between the graphs of

f x 0.5x 2x 4 and g x 2 4 4x x . Write, but do

not evaluate, a definite integral which represents:

a. the volume of a solid with base S if eac

h cross section of

the solid perpendicular to the x-axis is a semi-circle.

b. the volume generated by rotating region S around the line

y = 5.

24

0

g x f xdx

2 2

4

2 2

0

5 f x 5 g x dx

NO CALCULATORThe base of a solid is the region in the first quadrant bounded by

the curve y sinx for 0 x . If each cross section of the

solid perpendicular to the x-axis is a square, the volume of the

solid, in cu

bic units, is:

A. 0 B. 1 C. 2 D. 3 E. 4

2

0

0 0

sinx dx sinxdx cos x | 1 1 2 C

NO CALCULATORThe base of a solid is a right triangle whose perpendicular sides

have lengths 6 and 4. Each plane section of the solid perpendicular

to the side of length 6 is a semicircle whose diameter lies in the

plane of the triangle. The volume, in cubic units, of the solid is:

A. 2 B. 4 C. 8 D. 16 E. 24 2

6 62

0 0

3 60

2x1 13 dx x dx

2 2 18

x |544 B

Let R be the region in the first quadrant under the graph of

3

8y for 1, 8

x

a) Find the area of R.

b) The line x = k divides the region R into two regions. If the part of region R to the left of the line is 5/12 of the area of the whole region R, what is the value of k?

c) Find the volume of the solid whose base is the region R and whose cross sections cut by planes perpendicular to the x-axis are squares.

CALCULATOR REQUIRED

Let R be the region in the first quadrant under the graph of

3

8y for 1, 8

x

a) Find the area of R.

8

31

8dx 36

x

Let R be the region in the first quadrant under the graph of

3

8y for 1, 8

x

b) The line x = k divides the region R into two regions. If the part of region R to the left of the line is 5/12 of the area of the whole region R, what is the value of k?

k

31

8dx

x

A

536

12

2/ 3 k112x | 15

2/ 32k 11 12 5

k 3.375

Let R be the region in the first quadrant under the graph of

3

8y for 1, 8

x

c) Find the volume of the solid whose base is the region R and whose cross sections cut by planes perpendicular to the x-axis are squares.

28

21

8dx 192

x

Let R be the region in the first quadrant bounded above by thegraph of f(x) = 3 cos x and below by the graph of 2xg x e

a) Setup, but do not evaluate, an integral expression in terms of a single variable for the volume of the solid generated when R is revolved about the x-axis.

b) Let the base of a solid be the region R. If all cross sections perpendicular to the x-axis are equilateral triangles, setup, but do not evaluate, an integral expression of a single variable for the volume of the solid.

20.836 22 x

0

3cosx e dx

20.836 2

x

0

33cosx e dx

4