A _____ lens is used to converge light<br><br> A. Convex<br> B. Concave

A car driving on the highway is going 72mph After 3 hours how many miles will the car have driven ?

Sergeu [11.5K]

Answer:

216 miles

Explanation:

you times 72 by three

7 0

2 years ago

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Which statement best describes the relationship between an object's density and its index of refraction? as the optical density

babunello [35]

For future references, the answer is B.

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2 years ago

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Which of these ionic compounds have polyatomic ions? Check all that apply.

Taya2010 [7]

Answer:

CaCO₃ and
NaOH.

Explanation:

Polyatomic ions are ions that contain more than one atom in each one of the ions.

Ionic compounds are made of cations (positive ions) and anions (negative ion). By convention, the cation is written before the anion.

List the ions in each compound:

Cation: $\rm Ca^{2+}$ ,

Anion: $\rm {CO_3}^{2-}$ .

$\rm Ca^{2+}$ is a monatomic ion for it contains only one atom in each ion.

$\rm {CO_3}^{2-}$ is a polyatomic ion for it contains four atoms (one C atom and three O atoms) in each ion.

Cation: $\rm Na^{+}$ ,

Anion: $\rm F^{-}$ .

Both $\rm Na^{+}$ and $\rm F^{-}$ are monatomic for they contain only one atom in each ion.

Cation: $\rm Fe^{2+}$ ,

Anion: $\rm {O}^{2-}$ .

Both $\rm Fe^{2+}$ and $\rm O^{2-}$ are monatomic for they contain only one atom in each ion.

Cation: $\rm Ca^{2+}$ ,

Anion: $\rm {Cl}^{-}$ .

Both $\rm Ca^{2+}$ and $\rm Cl^{-}$ are monatomic for they contain only one atom in each ion.

Cation: $\rm Na^{+}$ ,

Anion: $\rm {OH}^{-}$ .

$\rm Na^{+}$ is a monatomic ion for it contains only one atom in each ion.

$\rm {OH}^{-}$ is a polyatomic ion for it contains two atoms (one O atom and one H atom) in each ion.

5 0

2 years ago

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(a) Consider the initial-value problem dA/dt = kA, A(0) = A0 as the model for the decay of a radioactive substance. Show that, i

murzikaleks [220]

Answer:

a) $t = -\frac{ln(2)}{k}$

b) See the proof below

$A(t) = A_o 2^{-\frac{t}{T}}$

c) $t = 3T \frac{ln(2)}{ln(2)}= 3T$

Explanation:

Part a

For this case we have the following differential equation:

$\frac{dA}{dt}= kA$

With the initial condition $A(0) = A_o$

We can rewrite the differential equation like this:

$\frac{dA}{A} =k dt$

And if we integrate both sides we got:

$ln |A|= kt + c_1$

Where $c_1$ is a constant. If we apply exponential for both sides we got:

$A = e^{kt} e^c = C e^{kt}$

Using the initial condition $A(0) = A_o$ we got:

$A_o = C$

So then our solution for the differential equation is given by:

$A(t) = A_o e^{kt}$

For the half life we know that we need to find the value of t for where we have $A(t) = \frac{1}{2} A_o$ if we use this condition we have:

$\frac{1}{2} A_o = A_o e^{kt}$

$\frac{1}{2} = e^{kt}$

Applying natural log we have this:

$ln (\frac{1}{2}) = kt$

And then the value of t would be:

$t = \frac{ln (1/2)}{k}$

And using the fact that $ln(1/2) = -ln(2)$ we have this:

$t = -\frac{ln(2)}{k}$

Part b

For this case we need to show that the solution on part a can be written as:

$A(t) = A_o 2^{-t/T}$

For this case we have the following model:

$A(t) = A_o e^{kt}$

If we replace the value of k obtained from part a we got:

$k = -\frac{ln(2)}{T}$

$A(t) = A_o e^{-\frac{ln(2)}{T} t}$

And we can rewrite this expression like this:

$A(t) = A_o e^{ln(2) (-\frac{t}{T})}$

And we can cancel the exponential with the natural log and we have this:

$A(t) = A_o 2^{-\frac{t}{T}}$

Part c

For this case we want to find the value of t when we have remaining $\frac{A_o}{8}$

So we can use the following equation:

$\frac{A_o}{8}= A_o 2^{-\frac{t}{T}}$

Simplifying we got:

$\frac{1}{8} = 2^{-\frac{t}{T}}$

We can apply natural log on both sides and we got:

$ln(\frac{1}{8}) = -\frac{t}{T} ln(2)$

And if we solve for t we got:

$t = T \frac{ln(8)}{ln(2)}$

We can rewrite this expression like this:

$t = T \frac{ln(2^3)}{ln(2)}$

Using properties of natural logs we got:

$t = 3T \frac{ln(2)}{ln(2)}= 3T$

8 0

3 years ago

If you double the voltage in a circuit and reduce the resistance by a factor of four, what will happen to the current?

Kamila [148]

<span>doubling or tripling the voltage will cause the current to be doubled or tripled. On the other hand, any alteration in the resistance will result in the opposite or inverse alteration of the current. So doubling or tripling the resistance will cause the current to be one-half or one-third the original value.</span>

5 0

2 years ago

A _____ lens is used to converge light A. Convex B. Concave