You paint 1/2 wall in 1/4 hour. At that rate, how long will it take you to paint one wall?

Evaluate the surface integral S F · dS for the given vector field F and the oriented surface S. In other words, find the flux of

tresset_1 [31]

Because I've gone ahead with trying to parameterize $S$ directly and learned the hard way that the resulting integral is large and annoying to work with, I'll propose a less direct approach.

Rather than compute the surface integral over $S$ straight away, let's close off the hemisphere with the disk $D$ of radius 9 centered at the origin and coincident with the plane $y=0$ . Then by the divergence theorem, since the region $S\cup D$ is closed, we have

$\displaystyle\iint_{S\cup D}\vec F\cdot\mathrm d\vec S=\iiint_R(\nabla\cdot\vec F)\,\mathrm dV$

where $R$ is the interior of $S\cup D$ . $\vec F$ has divergence

$\nabla\cdot\vec F(x,y,z)=\dfrac{\partial(xz)}{\partial x}+\dfrac{\partial(x)}{\partial y}+\dfrac{\partial(y)}{\partial z}=z$

so the flux over the closed region is

$\displaystyle\iiint_Rz\,\mathrm dV=\int_0^\pi\int_0^\pi\int_0^9\rho^3\cos\varphi\sin\varphi\,\mathrm d\rho\,\mathrm d\theta\,\mathrm d\varphi=0$

The total flux over the closed surface is equal to the flux over its component surfaces, so we have

$\displaystyle\iint_{S\cup D}\vec F\cdot\mathrm d\vec S=\iint_S\vec F\cdot\mathrm d\vec S+\iint_D\vec F\cdot\mathrm d\vec S=0$

$\implies\boxed{\displaystyle\iint_S\vec F\cdot\mathrm d\vec S=-\iint_D\vec F\cdot\mathrm d\vec S}$

Parameterize $D$ by

$\vec s(u,v)=u\cos v\,\vec\imath+u\sin v\,\vec k$

with $0\le u\le9$ and $0\le v\le2\pi$ . Take the normal vector to $D$ to be

$\vec s_u\times\vec s_v=-u\,\vec\jmath$

Then the flux of $\vec F$ across $S$ is

$\displaystyle\iint_D\vec F\cdot\mathrm d\vec S=\int_0^{2\pi}\int_0^9\vec F(x(u,v),y(u,v),z(u,v))\cdot(\vec s_u\times\vec s_v)\,\mathrm du\,\mathrm dv$

$=\displaystyle\int_0^{2\pi}\int_0^9(u^2\cos v\sin v\,\vec\imath+u\cos v\,\vec\jmath)\cdot(-u\,\vec\jmath)\,\mathrm du\,\mathrm dv$

$=\displaystyle-\int_0^{2\pi}\int_0^9u^2\cos v\,\mathrm du\,\mathrm dv=0$

$\implies\displaystyle\iint_S\vec F\cdot\mathrm d\vec S=\boxed{0}$

8 0

3 years ago

Kelly needs to order lunch for orders 6 people at a business meeting. Her menu choices are chicken salad for a cost of $5 per pe

nirvana33 [79]

Ok , with that information we can write the equations
x + y = 6
5x + 4y = 28

Where x = how many people ordered chicken
and y = how many people ordered egg salad

Through elimination , we can set one of the variables in both equations equal so we can eliminate it :

(4)x + (4)y = (4)6
5x + 4y = 28

4x + 4y = 24. equation 1
5x + 4y = 28. equation 2

Now we can subtract the second equation by the first equation and isolate one variable:
equation 2 - equation 1

5x - 4x + 4y - 4y = 28 - 24

x = 4

Now that we discovered our x value ( How many people ordered chicken salad ) , we can apply it to one of the equations and discover y ( how many people ordered egg salad)

x + y = 6
x= 4
4 + y = 6

We can shift 4 to the other side of the equation by subtracting 4 from both sides of the equation:
4 - 4 + y = 6 - 4
y = 2

x=4 and y=2

So the awnser is :
4 people ordered chicken salad and 2 people ordered egg salad!

I hope you understood my brief explanation!!

p.s if you want to know how to use another method to solve these problems ( Substition) , just let me know in a comentary down here

5 0

2 years ago

A company produces a 4.56×10 to the third power lightbulbs each week running in scientific notation which is the best estimate o

stepladder [879]

Answer:Production rate = 4.56 x 10³ bulbs/week

Production time = 9.36 x 10² weeks

Number of bulbs produced is

Answer: 4.27 x 10⁶ bulbs

Step-by-step explanation:

5 0

3 years ago

Abena has 1.3kg of apples and plenty of the other ingredients.

Sphinxa [80]

Answer:

No, she can't make for 15 people.

Step-by-step explanation:

For 15 people the mass of apple required is 1.375 kg.

She can only make 14 apple crumbles.

Please mark as brainliest

7 0

2 years ago

Help me plz it’s due today

professor190 [17]

Answer:

how to help u the picture is black

8 0

2 years ago