145 find 2 intergers

The surface area of a melting snowball decreases at a rate of3.8cm2/min. Find the rate at which its diameter decreases when the

Scorpion4ik [409]

Answer:

Step-by-step explanation:

This is a pretty basic related rates problem. I'm going to go through this just like I do in class when I'm teaching it to my students.

We see we have a snowball, which is a sphere. We are talking about the surface area of this sphere which has a formula of

$S=4\pi r^2$

In the problem we are given diameter, not radius. What we know about the relationship between a radius and a diameter is that

d = 2r so

$\frac{d}{2}=r$ Now we can have the equation in terms of diameter instead of radius. Rewriting:

$S=4\pi(\frac{d}{2})^2$ which simplifies to

$S=4\pi(\frac{d^2}{4})$ and a bit more to

$S=\pi d^2$ (the 4's cancel out by division). Now that is a simple equation for which we have to find the derivative with respect to time.

$\frac{dS}{dt}=\pi*2d\frac{dD}{dt}$ Now let's look at the problem and see what we are given as far as information.

The rate at which the surface area changes is -3.8, and we are looking for $\frac{dD}{dt}$ , the rate at which the diameter is changing, when the diameter is 13. Filling in:

$-3.8=\pi(2)(13)\frac{dD}{dt}$ and solving for the rate at which the diameter is changing:

$-\frac{3.8}{26\pi}=\frac{dD}{dt}$ and divide to get

$\frac{dD}{dt}=-.459\frac{cm}{min}$ Obviously, the negative means that the diameter is decreasing.

7 0

2 years ago

Differentiating a Logarithmic Function in Exercise, find the derivative of the function. See Examples 1, 2, 3, and 4.

wlad13 [49]

Answer:

$\frac{dy}{dx}=\frac{x(1-2lnx)}{x^{4}}$

Step-by-step explanation:

To solve the question we refresh our knowledge of the quotient rule.

For a function f(x) express as a ratio of another functions u(x) and v(x) i.e

$f(x)=\frac{u(x)}{v(x)}\\$ , the derivative is express as

$\frac{df(x)}{dx}=\frac{v(x)\frac{du(x)}{dx}-u(x)\frac{dv(x)}{dx}}{v(x)^{2} }$

from $y=lnx/x^{2}$

we assign u(x)=lnx and v(x)=x^2

and the derivatives

$\frac{du(x)}{dx}=\frac{1}{x}\\\frac{dv(x)}{dx}=2x\\$ .

Note the expression used in determining the derivative of the logarithm function.it was obtain from the general expression of logarithm derivative i.e $y=lnx\\\frac{dy}{dx}=\frac{1}{x}$

If we substitute values into the quotient expression we arrive at

$\frac{dy}{dx}=\frac{(x^{2}*\frac{1}{x})-(2x*lnx)}{x^{4}}\\\frac{dy}{dx}=\frac{x-2xlnx}{x^{4}}\\\frac{dy}{dx}=\frac{x(1-2lnx)}{x^{4}}$

8 0

2 years ago

Complete the following sentence.<br><br> A radius is________ <br> the diameter.

Ulleksa [173]

Answer:

1/2

Step-by-step explanation:

The radius is 1/2 of the diameter

4 0

2 years ago

Read 2 more answers

Hank's pickup can travel 80 miles on 5 gallons of gas. How many gallons will Hank's pickup need to travel 64 miles?

mr_godi [17]

Answer:

4 gallons

Step-by-step explanation:

80/5 will give you 16 so for each gallon the car can move 16 milles

so 64/16 = 4 so he will need 4 gallons of gas in order make the trip

4 0

2 years ago

Read 2 more answers

A football team lost five yards on each of two consecutive plays. Find the total change in yardage.

maria [59]

Answer:

The change is a loss of 10 yards, so -10 yards.

Step-by-step explanation:

The total change in yardage after 2 plays is the sum of the yardage of each play.

What lost yardage means?

Lost yardage means negative yardage.

Imagine that in a Buffalo Bills game, Devin Singletary lost 2 yards on his first carry. So his total yardage is -2.

If in the next carry he gets 3 yards, his total yardage is 1. If he loses 1, his total yardage is -3.

First play

Loss of 5 yards.

So the first play counts for -5 yards.

Second play

Loss of 5 yards.

So the second play counts for -5 yards.

Total

-5 - 5 = -10

The change is a loss of 10 yards, so -10 yards.

8 0

2 years ago