A central force is one of the form $\mathbf{F}=f(\|\mathbf{r}\|) \mathbf{r}$, where f has a continuous derivative (except possibly at $\|\mathbf{r}\|=0$ ). Show that the work done by such a force in moving an object around a closed path that misses the origin is 0.

In given problem, show that the given line integral is independent of path (use Theorem $\mathrm{C}$ ) and then evaluate the integral (either by choosing a convenient path or, if you prefer, by finding a potential function f and applying Theorem A).

$$\int_{(0,0,0)}^{(1,1,1)}\left(6 x y^3+2 z^2\right) d x+9 x^2 y^2 d y+(4 x z+1) d z$$

Hint: Try the path consisting of line segments from $(0,0,0)$ to $(1,0,0)$ to $(1,1,0)$ to $(1,1,1)$.

Let $\mathbf{F}=2 z \mathbf{i}+2 y \mathbf{k}$, and let $\partial S$ be the intersection of the cylinder $x^2+y^2=a y$ with the hemisphere $z=\sqrt{a^2-x^2-y^2}$, $a>0$. Assuming distances in meters and force in newtons, find the work done by the force $\mathbf{F}$ in moving an object around $\partial S$ in the counterclockwise direction as viewed from above.

Show that the work done by a constant force $\mathbf{F}$ in moving a body around a simple closed curve is 0.

Find the mass of a wire with the shape of the curve $y=x^2$ between (-2,4) and (2,4) if the density is given by $\delta(x, y)=$ k|x|.

In given problem, find div $\mathbf{F}$ and curl $\mathbf{F}$.

$$\mathbf{F}(x, y, z)=e^x \cos y \mathbf{i}+e^x \sin y \mathbf{j}+z \mathbf{k}$$

In given problem, show that the given line integral is independent of path (use Theorem $\mathrm{C}$ ) and then evaluate the integral (either by choosing a convenient path or, if you prefer, by finding a potential function f and applying Theorem A).

$$\int_{(-1,1)}^{(4,2)}\left(y-\frac{1}{x^2}\right) d x+\left(x-\frac{1}{y^2}\right) d y$$

If $\mathbf{F}=\left(x^2+y^2\right) \mathbf{i}+2 x y \mathbf{j}$, calculate the circulation of $\mathbf{F}$ around C of given problem; that is, calculate $\oint_C \mathbf{F} \cdot \mathbf{T} d s$.

Let $\mathbf{F}=2 \mathbf{i}+x z \mathbf{j}+z^3 \mathbf{k}$ and $\partial S$ be the boundary of the surface $z=x^2 y^2, x^2+y^2 \leq a^2$, oriented counterclockwise as viewed from above. Evaluate $\oint_{\partial S} \mathbf{F} \cdot \mathbf{T} d s$.

In given problem, evaluate each line integral.

Same integral as in previous problem; C is the line segment from (0,0,0) to (2,3,4).

Use the result of previous problem to verify the formula for the volume of a right circular cylinder of height h and radius a.

Find the center of mass of the homogeneous triangle with vertices (a, 0,0),(0, b, 0), and (0,0, c), where a,b, and c are all positive.

In given problem, find div $\mathbf{F}$ and curl $\mathbf{F}$.

$$\mathbf{F}(x, y, z)=\cos x \mathbf{i}+\sin y \mathbf{j}+3 \mathbf{k}$$

Let C be the circle that is the intersection of the plane $a x+b y+z=0(a \geq 0, b \geq 0)$ and the sphere $x^2+y^2+z^2=9$. For $\mathbf{F}=y \mathbf{i}-x \mathbf{j}+3 y \mathbf{k}$, evaluate

$$\oint_C \mathbf{F} \cdot \mathbf{T} d s$$

Hint: Use Stokes's Theorem.