You are driving along the coast at 45 mph. How many minutes should it take you to get to Ventura?

A breeder reactor converts uranium-238 into an isotope of plutonium-239 at a rate proportional to the amount of uranium-238 pres

topjm [15]

Let $U(t)$ denote the amount of uranium-238 in the reactor at time $t$ . As conversion to plutonium-239 occurs, the amount of uranium will decrease, so the conversion rate is negative. Because the rate is proportional to the current amount of uranium, we have

$\dfrac{\mathrm dU}{\mathrm dt}=-kU$

where $k>0$ is constant. Separating variables and integrating both sides gives

$\dfrac{\mathrm dU}U=-k\,\mathrm dt\implies\ln|U|=-kt+C\implies U=Ce^{-kt}$

Suppose we start some amount $u$ . This means that at time $t=0$ we have $U(0)=u$ , so that

$u=Ce^{-0k}\implies C=u\implies U=ue^{-kt}$

We're given that after 10 years, 99.97% of the original amount of uranium remains. This means (if $t$ is taken to be in years) for some starting amount $u$ ,

$0.9997u=ue^{-10k}\implies k=-\dfrac{\ln(0.9997)}{10}$

The half-life is the time $t_{1/2}$ it takes for the starting amount $u$ to decay to half, $0.5u$ :

$0.5u=ue^{-kt_{1/2}}\implies t_{1/2}=-\dfrac{\ln(0.5)}k=\dfrac{10\ln2}{\ln(0.9997)}$

or about 23,101 years. Notice that it doesn't matter what the actual starting amount is, the half-life is independent of that.

7 0

3 years ago

A bathtub can hold up to 70 gallons of water. The bath tub drains at a constant rate. when you first see the bath tub, it has 42

Darina [25.2K]

Answer:

A. 28

B. 1 min

C. 2 mins

Step-by-step explanation:

5 0

2 years ago

What is the rate of change and initial value for the linear relation that includes the points shown in the table? x; 1,3,5,7

BARSIC [14]

Answer:

The rate of change is -5

The initial value is 25

Step-by-step explanation:

Since, this is a linear relation

so, we can select any two points and find equation of line

points are (1,20) and (3,10)

so,

$x_1=1,y_1=20$

$x_2=3,y_2=10$

now, we can find slope

$m=\frac{y_2-y_1}{x_2-x_1}$

now, we can plug values

$m=\frac{10-20}{3-1}$

$m=-5$

now, we can use point slope form of line

$y-y_1=m(x-x_1)$

now, we can plug values

$y-20=-5(x-1)$

now, we can solve for y

$y=-5x+25$

we know that

slope is the rate of change

So, the rate of change is -5

For finding initial value , we can plug x=0 and find y

$y=-5\times 0+25$

$y=25$

So, initial value is 25

3 0

2 years ago

Proportions and Similarity

nekit [7.7K]

$\bf \cfrac{length}{width}\qquad \qquad \stackrel{A}{\cfrac{4}{5}}\qquad \stackrel{B}{\cfrac{20}{25}}\implies \cfrac{4}{5}\qquad \checkmark$

5 0

2 years ago

Find the area of an octagon whose perimeter is 120 cm.

stira [4]

Answer:

The area of an octagon whose perimeter is 120 cm is 1086.4 $cm^{2}$

Step-by-step explanation:

An octagon is a polygon with eight sides. If the lengths of all the sides and the measurement of all the angles are equal, the octagon is called a regular octagon.

There is a predefined set of formulas for the calculation of perimeter, and area of a regular octagon.

The perimeter of an Octagon is given by

$P=8a$