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3 years ago

The half-life for the radioactive decay of calcium-47 is 4.5 days. how many half-lives have elapsed after 27 days?

Chemistry

2 answers:

Evgesh-ka [11]3 years ago

8 0

1 half-life - 4.5 days
x half-lives - 27 days

x=(1*27)/4.5=6
6 half-lives have elapsed after 27 days.

Pani-rosa [81]3 years ago

6 0

Answer: The number of half lives are 6

Explanation:

We are given:

Half life of a radioactive isotope = 4.5 days

Calculating the number of half lives after time has elapsed 27 days:

4.5 days have been elapsed time after 1 half life

So, 27 days must have been elapsed after = $\frac{1}{4.5}\times 27=6$ half lives

Hence, the number of half lives are 6

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A sample of an ideal gas at 1.00 atm and a volume of 1.84 L was placed in a weighted balloon and dropped into the ocean. As the

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Answer:

0.0613 L

Explanation:

Given data

Initial pressure (P₁): 1.00 atm

Initial volume (V₁): 1.84 L

Final pressure (P₂): 30.0 atm

Final volume (V₂): ?

Since we are dealing with an ideal gas, we can calculate the final volume using Boyle's law.

P₁ × V₁ = P₂ × V₂

V₂ = P₁ × V₁ / P₂

V₂ = 1.00 atm × 1.84 L / 30.0 atm

V₂ = 0.0613 L

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Elena L [17]

HELP ME!!!
Project: Modeling potential and kinetic energy
Assignment Summary
For this assignment, you will develop a model that shows a roller coaster cart in four different positions on a track. You will then use this model to discuss the changes in potential and kinetic energy of the cart as it moves along the track.
Background Information
The two most common forms of energy are potential energy and kinetic energy. Potential energy is the stored energy an object has due to its position. Kinetic energy is the energy an object has due to its motion. An object’s kinetic energy changes with its motion, while its potential energy changes with its position, but the total energy stays the same. If potential energy increases, then kinetic energy decreases. If potential energy decreases, then kinetic energy increases.
Potential energy related to the height of an object is called gravitational potential energy. Gravitational potential energy is directly related to an object’s mass, the acceleration due to gravity, and an object’s height.
Materials
 One poster board per student  Drawing utensils
Assignment Instructions
Step 1: Prepare for the project.
a) Read the entire Student Guide before you begin this project.
b) If anything is unclear, be sure to ask your teacher for assistance before you begin.
c) Gather the materials you will need to complete this project.
Step 2: Create your poster.
a) On the poster board, draw a roller coaster track that starts with one large hill, then is followed by a valley and another, smaller hill.
b) Draw a cart in four positions on the track as outlined below.
i. Draw the first cart at the top of the first hill. Label it A.
ii. Draw the second cart going down the first hill into the valley. Label it B.
iii. Draw the third cart at the bottom of the valley. Assume that the height of the cart in this position is zero. Label it C.
iv. Draw the last cart at the top of the second, smaller hill. Label it D.
c) Make sure that your name is on the poster. Step 3: Type one to two paragraphs that describe the energy of the cart.
a) Type one to two paragraphs describing the changes in potential and kinetic energy of the cart. Be sure to discuss how the potential and kinetic energy of the cart changes at each of the four positions along the track, and explain why these changes occur.
b) Make sure your name is on the document.
c) Later, you will submit this document through the virtual classroom.
Step 4: Evaluate your project using this checklist.
If you can check each criterion below, you are ready to submit your project.
 Did you draw a model of a roller coaster track with one large hill, a valley, and a smaller hill?
 Did you draw a cart on the track in the four required positions A–D? Did you label the cart at each of the four positions?
 Did you type a paragraph describing the changes in potential and kinetic energy of the cart at each of the four positions on the roller coaster track? Did you explain why the changes in potential and kinetic energy occur?
Step 5: Revise and submit your project.
a) If you were unable to check off all of the requirements on the checklist, go back and make sure that your project is complete.
b) When you have completed your project, submit your poster to your teacher for grading. Be sure that your name is on it.
c) Submit the typewritten document through the virtual classroom. Be sure that your name is on it.
Step 6: Clean up your work space.
a) Clean up your work space. Return any reusable materials to your teacher and throw away any trash.
b) Congratulations! You have completed your project.
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3 years ago

An environmental scientist developed a new analytical method for the determination of cadmium (cd^2+) in mussels. To validate th

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Answer:

The method is accurate in the calculation of the $Cu^+2$

Explanation:

As a first step we have to calculate the average concentration of $Cu^+2$ find it by the method.

$\frac{0.782+0.762+0.825+0.838+0.761 }{5} =0.79 ppm$

Then we have to find the standard deviation:

$s=\sqrt{\frac{1}{N-1}\sum_{i=1}^N(x_i-\bar{x})^2}=0.0359$

For the confidence interval we have to use the formula:

μ=Average± $\frac{t*s}{\sqrt{n} }$

Where:

t=t student constant with 95 % of confidence and 5 data=2.78

μ= $0.79$ ± $\frac{2.78*0.0359}{\sqrt{5} }$

upper limit: 0.84

lower limit: 0.75

If we compare the limits of the value obtanied by the method (Figure 1 Red line) with the reference material (Figure 1 blue line) we can see that the values obtained by the method are within the values suggested by the reference material. So, it's method is accurate.