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Mathematics
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Multivariable Calculus International
Exam 8: Further Applications of Integration
Path 4
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Question 121
Short Answer
Set up, but do not evaluate, an integral for the area of the surface obtained by rotating the curve about the given axis.
y
=
e
x
,
1
≤
y
≤
9
;
y
-axis
y = e ^ { x } , 1 \leq y \leq 9 ; y \text {-axis }
y
=
e
x
,
1
≤
y
≤
9
;
y
-axis
Question 122
Short Answer
A swimming pool is
10
f
t
10 \mathrm { ft }
10
ft
wide and
36
f
t
36 \mathrm { ft }
36
ft
long and its bottom is an inclined plane, the shallow end having a depth of
4
f
t
4 \mathrm { ft }
4
ft
and the deep end,
12
f
t
12 \mathrm { ft }
12
ft
. If the pool is full of water, find the hydrostatic force on the shallow end. (Use the fact that water weighs
62.5
l
b
/
f
t
3
62.5 \mathrm { lb } / \mathrm { ft } ^ { 3 }
62.5
lb
/
ft
3
.)
Question 123
Multiple Choice
The standard deviation for a random variable with probability density function
f
f
f
and mean
μ
\mu
μ
is defined
σ
=
[
∫
−
∞
∞
(
x
−
μ
)
2
f
(
x
)
d
x
]
1
/
2
\sigma = \left[ \int _ { - \infty } ^ { \infty } ( x - \mu ) ^ { 2 } f ( x ) d x \right] ^ { 1 / 2 }
σ
=
[
∫
−
∞
∞
(
x
−
μ
)
2
f
(
x
)
d
x
]
1/2
Find the standard deviation for an exponential density function with mean
10.
10 .
10.
Question 124
Short Answer
A cylindrical drum of diameter
6
f
t
6 \mathrm { ft }
6
ft
and length
9
f
t
9 \mathrm { ft }
9
ft
is lying on its side, submerged in water
10
f
t
10 \mathrm { ft }
10
ft
deep. Find the force exerted by the water on one end of the drum to the nearest pound. (The weight density of water is
62.4
l
b
/
f
t
3
62.4 \mathrm { lb } / \mathrm { ft } ^ { 3 }
62.4
lb
/
ft
3
.)
Question 125
Multiple Choice
Find the area of the surface obtained by revolving the given curve about the
x
x
x
-axis.
y
=
e
x
+
e
−
x
2
y = \frac { e ^ { x } + e ^ { - x } } { 2 }
y
=
2
e
x
+
e
−
x
on
[
0
,
ln
3
]
[ 0 , \ln 3 ]
[
0
,
ln
3
]
Question 126
Short Answer
Find the area of the surface obtained by revolving the given curve about the
x
x
x
-axis.
y
=
e
x
+
e
−
x
2
on
[
0
,
ln
5
]
y = \frac { e ^ { x } + e ^ { - x } } { 2 } \text { on } [ 0 , \ln 5 ]
y
=
2
e
x
+
e
−
x
on
[
0
,
ln
5
]
Question 127
Short Answer
Set up, but do not evaluate, an integral for the length of the curve.
y
=
x
5
−
x
3
,
0
≤
x
≤
9
y = x \sqrt [ 3 ] { 5 - x } , 0 \leq x \leq 9
y
=
x
3
5
−
x
,
0
≤
x
≤
9
Question 128
Short Answer
Let
f
(
x
)
=
2
c
(
1
+
x
2
)
f ( x ) = \frac { 2 c } { \left( 1 + x ^ { 2 } \right) }
f
(
x
)
=
(
1
+
x
2
)
2
c
a) For what value of
c
c
c
is
f
f
f
a probability density function? b) For that value of
c
c
c
, find
P
(
−
1
<
X
<
1
)
P ( - 1 < X < 1 )
P
(
−
1
<
X
<
1
)
.
Question 129
Short Answer
A trough is filled with a liquid of density
855
k
g
/
m
3
855 \mathrm {~kg} / \mathrm { m } ^ { 3 }
855
kg
/
m
3
. The ends of the trough are equilateral triangles with sides
6
m
6 \mathrm {~m}
6
m
long and vertex at the bottom. Find the hydrostatic force on one end of the trough.
Question 130
Multiple Choice
Suppose the average waiting time for a customer's call to be answered by a company representative (modeled by exponentially decreasing probability density functions) is 20 minutes. Find the median waiting time.