# Thomas Calculus 12

## Educators

KF
SN
+ 3 more educators

### Problem 1

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=t \mathbf{i}+(1-t) \mathbf{j}, \quad 0 \leq t \leq 1$$

Check back soon!

### Problem 2

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=\mathbf{i}+\mathbf{j}+t \mathbf{k}, \quad-1 \leq t \leq 1$$

Check back soon!

### Problem 3

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=(2 \cos t) \mathbf{i}+(2 \sin t) \mathbf{j}, \quad 0 \leq t \leq 2 \pi$$

Check back soon!

### Problem 4

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=t \mathbf{i}, \quad-1 \leq t \leq 1$$

Check back soon!

### Problem 5

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=t \mathbf{i}+t \mathbf{j}+t \mathbf{k}, \quad 0 \leq t \leq 2$$

Check back soon!

### Problem 6

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=t \mathbf{j}+(2-2 t) \mathbf{k}, \quad 0 \leq t \leq 1$$

Check back soon!

### Problem 7

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=\left(t^{2}-1\right) \mathbf{j}+2 t \mathbf{k}, \quad-1 \leq t \leq 1$$

Check back soon!

### Problem 8

Match the vector equations in Exercises 1-8 with the graphs (a)-(h) given here.
$$\mathbf{r}(t)=(2 \cos t) \mathbf{i}+(2 \sin t) \mathbf{k}, \quad 0 \leq t \leq \pi$$

Check back soon!

### Problem 9

Evaluate $\int_{C}(x+y) d s$ where $C$ is the straight-line segment $x=t, y=(1-t), z=0,$ from $(0,1,0)$ to $(1,0,0)$

Check back soon!

### Problem 10

Evaluate $\int_{C}(x-y+z-2) d s$ where $C$ is the straight-line segment $x=t, y=(1-t), z=1,$ from $(0,1,1)$ to $(1,0,1)$

Check back soon!

### Problem 11

Evaluate $\int_{C}(x y+y+z) d s$ along the curve $\mathbf{r}(t)=2 t \mathbf{i}+$ $t \mathbf{j}+(2-2 t) \mathbf{k}, 0 \leq t \leq 1$

Check back soon!

### Problem 12

Evaluate $\int_{C} \sqrt{x^{2}+y^{2}} d s$ along the curve $\mathbf{r}(t)=(4 \cos t) \mathbf{i}+$ $(4 \sin t) \mathbf{j}$ $+3 t \mathbf{k},-2 \pi \leq t \leq 2 \pi.$

Check back soon!

### Problem 13

Find the line integral of $f(x, y, z)=x+y+z$ over the straightline segment from $(1,2,3)$ to $(0,-1,1)$ .

Check back soon!

### Problem 14

Find the line integral of $f(x, y, z)=\sqrt{3} /\left(x^{2}+y^{2}+z^{2}\right)$ over the curve $\mathbf{r}(t)=t \mathbf{i}+t \mathbf{j}+t \mathbf{k}, 1 \leq t \leq \infty$

Check back soon!

### Problem 15

Integrate $f(x, y, z)=x+\sqrt{y}-z^{2}$ over the path from $(0,0,0)$ to $(1,1,1)$ ( see accompanying figure) given by
$$C_{1} : \quad \mathbf{r}(t)=t \mathbf{i}+t^{2} \mathbf{j}, \quad 0 \leq t \leq 1$$
$$C_{2} : \quad \mathbf{r}(t)=\mathbf{i}+\mathbf{j}+t \mathbf{k}, \quad 0 \leq t \leq 1$$

Check back soon!

### Problem 16

Integrate $f(x, y, z)=x+\sqrt{y}-z^{2}$ over the path from $(0,0,0)$ to $(1,1,1)($ see accompanying figure) given by
$$C_{1} : \quad \mathbf{r}(t)=t \mathbf{k}, \quad 0 \leq t \leq 1$$
$$C_{2} : \quad \mathbf{r}(t)=t \mathbf{j}+\mathbf{k}, \quad 0 \leq t \leq 1$$
$$C_{3} : \quad \mathbf{r}(t)=t \mathbf{i}+\mathbf{j}+\mathbf{k}, \quad 0 \leq t \leq 1$$

Rebecca P.

### Problem 17

Integrate $f(x, y, z)=(x+y+z) /\left(x^{2}+y^{2}+z^{2}\right)$ over the path $\mathbf{r}(t)=t \mathbf{i}+t \mathbf{j}+t \mathbf{k}, 0 < a \leq t \leq b$

Check back soon!

### Problem 18

Integrate $f(x, y, z)=-\sqrt{x^{2}+z^{2}}$ over the circle
$$\mathbf{r}(t)=(a \cos t) \mathbf{j}+(a \sin t) \mathbf{k}, \quad 0 \leq t \leq 2 \pi$$

Chris T.

### Problem 19

Evaluate $\int_{C} x d s,$ where $C$ is
a. the straight-line segment $x=t, y=t / 2,$ from $(0,0)$ to $(4,2) .$
b. the parabolic curve $x=t, y=t^{2},$ from $(0,0)$ to $(2,4)$

Check back soon!

### Problem 20

Evaluate $\int_{C} \sqrt{x+2 y} d s,$ where $C$ is
a. the straight-line segment $x=t, y=4 t,$ from $(0,0)$ to $(1,4)$ .
b. $C_{1} \cup C_{2} ; C_{1}$ is the line segment from $(0,0)$ to $(1,0)$ and $C_{2}$ is the line segment from $(1,0)$ to $(1,2)$

Check back soon!

### Problem 21

Find the line integral of $f(x, y)=y e^{x^{2}}$ along the curve $\mathbf{r}(t)=4 t \mathbf{i}-3 t \mathbf{j},-1 \leq t \leq 2$

Check back soon!

### Problem 22

Find the line integral of $f(x, y)=x-y+3$ along the curve $\mathbf{r}(t)=(\cos t) \mathbf{i}+(\sin t) \mathbf{j}, 0 \leq t \leq 2 \pi$

Check back soon!

### Problem 23

Evaluate $\int_{C} \frac{x^{2}}{y^{4 / 3}} d s,$ where $C$ is the curve $x=t^{2}, y=t^{3},$ for $1 \leq t \leq 2$

KF
Kyle F.

### Problem 24

Find the line integral of $f(x, y)=\sqrt{y} / x$ along the curve $\mathbf{r}(t)=t^{3} \mathbf{i}+t^{4} \mathbf{j}, 1 / 2 \leq t \leq 1$

Check back soon!

### Problem 25

Evaluate $\int_{C}(x+\sqrt{y}) d s$ where $C$ is given in the accompanying figure.

Check back soon!

### Problem 26

Evaluate $\int_{C} \frac{1}{x^{2}+y^{2}+1} d s$ where $C$ is given in the accompanying figure.

SN
Skyler N.

### Problem 27

In Exercises $27-30,$ integrate $f$ over the given curve.
$$f(x, y)=x^{3} / y, \quad C : \quad y=x^{2} / 2, \quad 0 \leq x \leq 2$$

Check back soon!

### Problem 28

In Exercises $27-30,$ integrate $f$ over the given curve.
$$f(x, y)=\left(x+y^{2}\right) / \sqrt{1+x^{2}}, \quad C : \quad y=x^{2} / 2 from (I, 1/2) to (0,0)$$

Check back soon!

### Problem 29

In Exercises $27-30,$ integrate $f$ over the given curve.
$f(x, y)=x+y, \quad C : x^{2}+y^{2}=4$ in the first quadrant from (2, 0) to (0, 2)

Tanishq G.

### Problem 30

In Exercises $27-30,$ integrate $f$ over the given curve.
$$f(x, y)=x^{2}-y, \quad C : \quad x^{2}+y^{2}=4 in the first quadrant from (0,2) to (\sqrt{2}, \sqrt{2})$$

Tanishq G.

### Problem 31

Find the area of one side of the "winding wall" standing orthogonally on the curve $y=x^{2}, 0 \leq x \leq 2,$ and beneath the curve on the surface $f(x, y)=x+\sqrt{y}$

HN
Harrison N.

### Problem 32

Find the area of one side of the "wall" standing orthogonally on the curve $2 x+3 y=6,0 \leq x \leq 6,$ and beneath the curve on the surface $f(x, y)=4+3 x+2 y$

Check back soon!

### Problem 33

Mass of a wire Find the mass of a wire that lies along the curve $\mathbf{r}(t)=\left(t^{2}-1\right) \mathbf{j}+2 t \mathbf{k}, 0 \leq t \leq 1,$ if the density is $\delta=(3 / 2) t$

Check back soon!

### Problem 34

Center of mass of a curved wire A wire of density $\delta(x, y, z)=15 \sqrt{y+2}$ lies along the curve $\mathbf{r}(t)=\left(t^{2}-1\right) \mathbf{j}+$ $2 t \mathbf{k},-1 \leq t \leq 1 .$ Find its center of mass. Then sketch the curve and center of mass together.

Caleb H.

### Problem 35

Mass of with variable density wire lying along the curve $\mathbf{r}(t)=\sqrt{2} t \mathbf{i}+\sqrt{2} t \mathbf{j}+\left(4-t^{2}\right) \mathbf{k}$ $0 \leq t \leq 1,$ if the density is $(\mathbf{a}) \delta=3 t$ and $(\mathbf{b}) \delta=1$

Eric J.

### Problem 36

Center of mass of wire with variable density Find the center of mass of a thin wire lying along the curve $\mathbf{r}(t)=t \mathbf{i}+2 t \mathbf{j}+$ $(2 / 3) t^{3 / 2} \mathbf{k}, 0 \leq t \leq 2,$ if the density is $\delta=3 \sqrt{5}+t$

Check back soon!

### Problem 37

Moment of inertia of wire hoop A circular wire hoop of constant density $\delta$ lies along the circle $x^{2}+y^{2}=a^{2}$ in the $x y-$ plane. Find the hoop's moment of inertia about the $z$ -axis.

Check back soon!

### Problem 38

Inertia of a slender rod A slender rod of constant density lies along the line segment $\mathbf{r}(t)=t \mathbf{j}+(2-2 t) \mathbf{k}, 0 \leq t \leq 1,$ in the $y z$ -plane. Find the moments of inertia of the rod about the three coordinate axes.

Check back soon!

### Problem 39

Two springs of constant density A spring of constant density $\delta$ lies along the helix
$$\mathbf{r}(t)=(\cos t) \mathbf{i}+(\sin t) \mathbf{j}+t \mathbf{k}, \quad 0 \leq t \leq 2 \pi$$
a. Find $I_{z}$
b. Suppose that you have another spring of constant density $\delta$ that is twice as long as the spring in part (a) and lies along the helix for $0 \leq t \leq 4 \pi .$ Do you expect $I_{z}$ for the longer spring to be the same as that for the shorter one, or should it be different? Check your prediction by calculating $I_{z}$ for the longer spring.

Check back soon!

### Problem 40

Wire of constant density A wire of constant density $\delta=1$ lies along the curve
$$\mathbf{r}(t)=(t \cos t) \mathbf{i}+(t \sin t) \mathbf{j}+(2 \sqrt{2} / 3) t^{3 / 2} \mathbf{k}, \quad 0 \leq t \leq 1.$$

Check back soon!

### Problem 41

The arch in Example 3 Find $I_{x}$ for the arch in Example $3 .$

Tanishq G.

### Problem 42

Center of mass and moments of inertia for wire with variable density Find the center of mass and the moments of inertia about the coordinate axes of a thin wire lying along the curve
$$\mathbf{r}(t)=t \mathbf{i}+\frac{2 \sqrt{2}}{3} t^{3 / 2} \mathbf{j}+\frac{t^{2}}{2} \mathbf{k}, \quad 0 \leq t \leq 2$$
if the density is $\delta=1 /(t+1)$

Check back soon!

### Problem 43

In Exercises $43-46,$ use a CAS to perform the following steps to evaluate the line integrals.
a. Find $d s=|\mathbf{v}(t)| d t$ for the path $\mathbf{r}(t)=g(t) \mathbf{i}+h(t) \mathbf{j}+$ $k(t) \mathbf{k} .$
b. Express the integrand $f(g(t), h(t), k(t))|\mathbf{v}(t)|$ as a function of the parameter $t .$
c. Evaluate $\int_{C} f d s$ using Equation $(2)$ in the text.
$$f(x, y, z)=\sqrt{1+30 x^{2}+10 y} ; \quad \mathbf{r}(t)=t \mathbf{i}+t^{2} \mathbf{j}+3 t^{2} \mathbf{k} 0 \leq t \leq 2$$

Tanishq G.

### Problem 44

In Exercises $43-46,$ use a CAS to perform the following steps to evaluate the line integrals.
a. Find $d s=|\mathbf{v}(t)| d t$ for the path $\mathbf{r}(t)=g(t) \mathbf{i}+h(t) \mathbf{j}+$ $k(t) \mathbf{k} .$
b. Express the integrand $f(g(t), h(t), k(t))|\mathbf{v}(t)|$ as a function of the parameter $t .$
c. Evaluate $\int_{C} f d s$ using Equation $(2)$ in the text.
$$f(x, y, z)=\sqrt{1+x^{3}+5 y^{3}} ; \quad \mathbf{r}(t)=t \mathbf{i}+\frac{1}{3} t^{2} \mathbf{j}+\sqrt{t} \mathbf{k} 0 \leq t \leq 2$$

Tanishq G.

### Problem 45

In Exercises $43-46,$ use a CAS to perform the following steps to evaluate the line integrals.
a. Find $d s=|\mathbf{v}(t)| d t$ for the path $\mathbf{r}(t)=g(t) \mathbf{i}+h(t) \mathbf{j}+$ $k(t) \mathbf{k} .$
b. Express the integrand $f(g(t), h(t), k(t))|\mathbf{v}(t)|$ as a function of the parameter $t .$
c. Evaluate $\int_{C} f d s$ using Equation $(2)$ in the text.
$$f(x, y, z)=x \sqrt{y}-3 z^{2} ; \quad \mathbf{r}(t)=(\cos 2 t) \mathbf{i}+(\sin 2 t) \mathbf{j}+5 t \mathbf{k} 0 \leq t \leq 2 \pi$$

Tanishq G.
In Exercises $43-46,$ use a CAS to perform the following steps to evaluate the line integrals.
a. Find $d s=|\mathbf{v}(t)| d t$ for the path $\mathbf{r}(t)=g(t) \mathbf{i}+h(t) \mathbf{j}+$ $k(t) \mathbf{k} .$
b. Express the integrand $f(g(t), h(t), k(t))|\mathbf{v}(t)|$ as a function of the parameter $t .$
c. Evaluate $\int_{C} f d s$ using Equation $(2)$ in the text.
$$f(x, y, z)=\left(1+\frac{9}{4} z^{1 / 3}\right)^{1 / 4} ; \quad \mathbf{r}(t)=(\cos 2 t) \mathbf{i}+(\sin 2 t) \mathbf{j}+ t^{5 / 2} \mathbf{k}, \quad 0 \leq t \leq 2 \pi$$