Monday

September 22, 2014

September 22, 2014

Number of results: 67,493

**Physics**

An industrial worker accidentally inhaled a radioisotope with an activity of 0.200 kBq. The substance swallowed has a very long effective half-life and therefore the activity will not change significantly during the workerâ€™s lifetime. Every decay of the isotope releases 1.12...
*May 16, 2010 by Kirsten*

**Physics**

An industrial worker accidentally inhaled a radioisotope with an activity of 0.200 kBq. The substance swallowed has a very long effective half-life and therefore the activity will not change significantly during the workers lifetime. Every decay of the isotope releases 1.12 x ...
*May 17, 2010 by Anonymous*

**Chemistry**

Strontium-85, used for bone scans, has a half-life of 64 {\rm d}.How long will it take for the radiation level of strontium-85 to drop to \frac{1}{8} of its original level?
*April 27, 2011 by Help!!*

**Biology**

The half life of carbon 14 is 5700 years. If the carbon 14 level measured in a fossilized bone has only 1/4 of the original amount, how old in the bone?
*May 16, 2011 by Jennifer*

**Math/Calculus**

After 5 days, a particular radioactive substance decays to 37% of its original amount. Find the half life of this substance. Is this right? Th= ln 2/ln(1/.37) x 5 days
*October 17, 2011 by Christine*

**Biology**

The half-life of carbon-14 is 5,700 years. If a sample originally had 26 g of carbon-14, how much would it contain after 22,800 years?
*November 19, 2013 by Emily*

**biology**

What geological process is used to explain how nearly identical animals that cannot swim, are found on continents separated by large oceans? What is the half-life of Uranium 238 and what did we use that radioisotope to date as the oldest item on Earth?
*April 21, 2012 by Anonymous*

**writing**

do you think that life on earth could become this difficult during your life time?what factor could cause to take place ?a story about that shows what life might be like in the world?
*January 1, 2013 by Eduarda*

**liteature**

In The Call of the Wild, when London writes about "what a puppet thing life is," it reflects the theme summarized in which of the following statements? A. Our lives are lived in response to our predetermined fate. B. The course of a life is determined by pure chance. C. Each ...
*April 14, 2009 by victoria*

**Literature**

In The Call of the Wild, when London writes about "what a puppet thing life is," it reflects the theme summarized in which of the following statements? A. Our lives are lived in response to our predetermined fate. B. Each life pits mercy against nature. C. Every life is based ...
*September 24, 2012 by Sara Beth*

**Chemistry**

The reaction 2B--->C + 2D is found to be zero order when run at 990 degrees C. If it takes 3.3X110^2 s for an initial concentration of B to go from 0.50 M to .20 M what is the rate constant for the reaction? what is the half life of the reaction under these conditions?
*February 29, 2008 by Lauren*

**Math**

A bone is found to have 45% of the original amount of carbon 14. If the half life of carbon is 5600 years, how old is the bone. Would I use the formula N=No e^kt?
*November 20, 2010 by Hannah*

**calculus**

How do I set-up/solve this problem? Please help me. The half-life of the radioactive isotope gallium-70 is 20 minutes. If the initial amount of gallium-70 is 25 milligrams, when will 10 milligrams be left?
*February 17, 2011 by Melody*

**math**

How do I set-up/solve this problem? Please help me. The half-life of the radioactive isotope gallium-70 is 20 minutes. If the initial amount of gallium-70 is 25 milligrams, when will 10 milligrams be left?
*February 17, 2011 by Amy*

**Pre Calculus**

Exponential growth and decay find the half life of a radioactive substance if 220 grams of the substance decays to 200 grams in 4 years?
*October 25, 2011 by Josh*

**Chemistry**

A decomposition reaction has a rate constant of 0.0019 yr -1. ( a) What is the half-life of the reaction? ______ yr (b) How long does it take for [reactant] to reach 12.5% of its original value? ______ yr
*December 2, 2011 by Sam*

**Chemistry**

Radium-223 has a half-life of 11.4 days.Approximately how long would it take for the activity of a sample of Radium-223 to decrease to 1.00% of its initial value?
*March 1, 2013 by Michelle*

**A.P. Chemistry**

Thorium-232 undergoes alpha decay and has a half-life of 1.4 * 10^10 years. How long will it take for a 1.00mg sample of thorium-232 to be reduced to 0.5mg?
*April 25, 2013 by John*

**chem**

A typical dose of a radioactive sample is 27.0 mCi. How long does it take for the activity to reduce to 0.100 mCi? The half life of the sample is 211,000 y.
*September 19, 2014 by bekah*

**mathematics**

what is the equation for exponetial decay(radioactive decay) and how to use the half life in the equation
*November 2, 2011 by anonymous*

**college algebra**

Use a calculator to help solve the problem. An isotope of lead, 201Pb, has a half-life of 8.4 hours. How many hours ago was there 40% more of the substance? (Round your answer to one decimal place.) ____hr
*November 18, 2013 by Dee*

**physics**

how to i find average speed? the problem says. a driver set outa journey for the first half she drives at 30mi/h and second half 60mi/h. Find the driver's average speed?
*October 17, 2007 by Ron*

**Science HELP 2nd question**

A sample originally contained 2.5 g of rubidium 87 now contains 1.25 g. The half life of rubidium - 87 is 6 x 10 ( to the 10th) years. How old is teh sample? Is this possible? why or why not?
*February 8, 2008 by sam*

**Chemistry**

The half-life of oxygen -15 is 124 seconds. If a sample of oxygen -15 has an activity of 4000 becquerels, how many minutes will elapse before it reaches an acivity of 500 becquerels
*July 20, 2010 by Elisabeth*

**calculus**

Assume a substance has a half-life of 11 years and the initial amount is 144 grams. How much remains at the end of 5 years? How long will it be until only 30 % remains?
*September 14, 2010 by nick*

**chemistry**

A radioactive sample contains 2.45g of an isotope wiht a half life of 3.8 days. How much of the isotope in grams remains after 11.4 days? please explain
*November 26, 2011 by Monique*

**math**

A material has a half-life of 12 hours. If initially there are 4 grams of the material, how much is present after 8 hours? I know the answer is 8/3, but how would you solve this using calculus? please help.
*November 11, 2012 by alex*

**math**

A quantity of oxygen gas had 16.32 g of the radioactive isotope oxygen-19 in it. When measured exactly 10 minutes later, the amount of oxygen-19 was 0.964 g. What is the half-life, in seconds, of oxygen-19?
*March 17, 2013 by Matthew*

**PHYSICS **

A 5.30-g lead bullet traveling at 390 m/s is stopped by a large tree. If half the kinetic energy of the bullet is transformed into internal energy and remains with the bullet while the other half is transmitted to the tree, what is the increase in temperature of the bullet?
*November 26, 2012 by please help *

**Science**

A star's life depends on mass ___ mass=Long life Large mass= ____ life Small mass is long life and large mass is short life?
*August 28, 2014 by Coleson*

**science**

If the half-life of a 20.0g is known to be 24 minutes, how long will it take for only 5.0 grams of the sample to remain A.6 minutes B.24 minutes C.48 minutes D.96 minutes I NEED HELP!!!!
*September 25, 2013 by amor*

**science**

A British Concorde (BC) and a French Concorde (FC) flew in opposite directions around the earth (40 000 km). The BC covered half of its flight distance at a supersonic speed of 2500 km/h and the other half at a subsonic speed of 1000 km/h. The FC spent half of its flight time ...
*February 8, 2014 by king12*

**Chemistry re-post**

I took a look at this question to see if I copied it correctly, and it does NOT say how much of the solution was used. It does use mols as the unit. Dr. Bob, I am not sure what you mean by "decays into Argon." I realize that the 38 CL decays to Argon, but how would that work ...
*July 23, 2013 by Nancy *

**college physics**

By immersing a crown in water its volume is 26inc^3=4.2x10^-4m^3. what would its weight be if it were pure gold? What would its weight be if its volume were half gold and half lead?
*October 1, 2012 by tiffany*

**Precalculus**

The burial cloth of an Egyptian mummy is estimated to contain 57% of the carbon-14 it contained originally. How long ago was the mummy buried? (The half-life of carbon-14 is 5730 years.)
*June 10, 2010 by Miguel*

**Precalculus**

The burial cloth of an Egyptian mummy is estimated to contain 57% of the carbon-14 it contained originally. How long ago was the mummy buried? (The half-life of carbon-14 is 5730 years.)
*June 10, 2010 by Miguel*

**Intro to Astronomy**

The half-life of carbon 14, which is commonly used to date organic materials, is 5700 years. What is the minimum age of sample in which less than 1% of the organic carbon 14 is left?
*February 9, 2012 by M.T.*

**Maths**

Trudy brought a large bag of wine gums to school. She gave half to the first student she met, half the remainder to the next and half of what she had left to the third student. The last 5 wine gums she ate. How many were in the packet?
*March 2, 2009 by Jessika.*

**life!+ english!**

“What he could do he did.” How does this statement relate to our lives? I think what the teacher meant is, "How does that statement relate to your life?" This is something you need to answer for yourself. I cannot relate it to your life. You might be able to relate to it ...
*November 29, 2006 by harley!*

**Math**

Paul's car can have wheel's ranging from 18-24 inches radius. He has the option of getting a wheel with the diameter of 2 and half feet, 3 and half feet, or 4 and half feet. What size wheel should he purchase? Explain?
*April 9, 2012 by Ronasia Mcbride*

**HUMAN LIFE**

I have to do a project about the human life cylce dose anyone know any good websites or any good information about the seven stages of life or the human life span???? PLZZ HELP ME IT IS DUE THIS WEDNESDAY CAN SOMEONE PLZZZ HELP ME PLZZZZ
*March 8, 2010 by Rachael.gardner*

**physics- cat**

A cat usually lands on its feet regardless of the position from which it is dropped. A slow-motion film of a cat falling shows that the upper half of its body twists in one direction while the lower half twists in the opposite direction. Why does this type of rotation occur?
*June 16, 2010 by lau*

**Maths**

Mrs Smith pays kate for babysitting by giving her 10 cents for the first-half hour, 20 cents for the second half-hour, 40 cents for the third half-hour etc. How long does she work to earn $12.70?
*June 20, 2011 by Annabella Richards*

**physics**

A cat usually lands on its feet regardless of the position from which it is dropped. A slow-motion film of a cat falling shows that the upper half of its body twists in one direction while the lower half twists in the opposite direction. (See figure below.) Why does this type ...
*November 5, 2013 by suzyq*

**physics**

A fox is chasing a bunny. The bunny is initially hopping east at 7 m/s when it first sees the fox. Over the next half second the bunny changes its velocity to west at 12 m/s and escapes. What was the bunny's average acceleration (magnitude and direction) during this half-...
*October 10, 2012 by Patsy*

**Physics**

A runner covers one lap of a circular track 40.0 in diameter in 63.3 . For that lap, what was her average velocity? If she covered the first half-lap in 28.6 , what were her average velocity for that half-lap?
*February 6, 2013 by Anonymous*

**Chemistry**

Consider a certain type of nucleus that has a half life of 32 min. Calculate the percent of original sample of nucleus remaining after 3.0 hours have passed? how would i calculate this???
*March 4, 2008 by Gabe*

**chemistry**

Gallium-67 is used medically in tumor-seeking agents. The half-life of gallium-67 is 78.2 hours. If you begin with 36.6 mg of this isotope, what mass remains after 190 hours have passed?
*September 15, 2010 by fatin*

**Chemistry**

The half-life for radioactive decay of 14C is 5730 years (it emits β-particles with energy of 0.16 MeV). An archaeological sample contained wood that had only 72% of the 14C found in living trees. What is its age?
*April 8, 2010 by Zoa*

**Chemistry**

The given reaction, 2N2O5 4NO2 + O2, follows first-order kinetics and has an activation energy of 103 kJ mol-1. At 298 K, k = 0.0000354 s-1. What is the half-life (min) for this reaction at 338 K ? Round your answer to 3 significant figures.
*November 11, 2010 by Kyo*

**CHEM**

Pu-239 has a half-life of 24110 y. If 1.00 kg of this isotope is present in the used fuel rods of a nuclear power plant approximately how long will it take for this amount of Pu-239 to decay until there is less than 1 mg left ? Please help. I do not know how to do this question.
*March 14, 2012 by ARIANA*

**chemistry**

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 {\rm hr} and is a pure gamma emitter. Suppose that 280{\rm mg} were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals?
*September 26, 2012 by Shay*

**chemistry**

Technetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 {\rm hr} and is a pure gamma emitter. Suppose that 280{\rm mg} were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals?
*September 26, 2012 by Shay*

**Math**

I have a question: How would you solve this? a dozen dozen apples at half a dozen dimes a dozen? In this cause is dozen 12? And half a dozen dimes in 60 cents? would that be 120? b/c a dozen dozen is 24 so u have 24 apples and then you have 60 cents per dozen so two dozen ...
*December 5, 2006 by Gina*

**Physics**

A parallel-plate capacitor is made from two plates 12.0cm on each side and 4.50mm apart. Half of the space between these plates contains only air, but the other half is filled with Plexiglas of dielectric constant 3.40. An 18.0 V battery is connected across the plates. What is...
*March 3, 2011 by Rachel*

**12th grade**

The radioactive isotope of Carcon (^14C)has a half life of 5730. What is the decay constant of ^14C? If we start with a sample of 1000 carcon nuclei, how many will be left in 22920 years time?
*April 8, 2010 by Moe*

**Pre-Cal**

The radioactive isotope of Carcon (^14C)has a half life of 5730. What is the decay constant of ^14C? If we start with a sample of 1000 carcon nuclei, how many will be left in 22920 years time?
*April 8, 2010 by Moe*

**Physical Science**

Tritium (half-life= 12.3 y) is used to verify the age of expensive brandies. If an old brandy contains only 1/16 of the tritium present in new brandy, how long ago was it produced?
*October 29, 2010 by Angelica Mendoza*

**AP Environmental Science (URGENT)**

Strontium-90 is a radioactive waste product from nuclear reactors. It has a half-life of 29 years. How many years will it take for a quantity of strontium-90 to decay to 1/16 (one-sixteenth) of its original mass?
*January 11, 2012 by Heather*

**Math**

A drug is eliminated from bloodstream exponentially with half life of 48hours. If patient receives initial dose of 15 milligrams at midnight, how much of drug is in patient's blood at noon the next day?
*December 14, 2013 by Clare*

**chem**

Radioactive substances decay by first-order kinetics. How many years would be required for a sample containing strontium-90 to decrease to 58.32% of its initial activity? The half-life of strontium-90 is 2.88e1 years.
*February 22, 2014 by sara*

**Chemistry**

32P is a radioactive isotope with a half-life of 14.3 days. If you currently have 48.1 g of 32P, how much 32P was present 3.00 days ago?
*June 10, 2012 by Anonymous*

**Chemistry**

A reaction is first order in A. If the rate constant of the reaction is 3.45x10^-3 s-1, what is the half life of the reaction? a. 4.98x10^-3 s b. 200 s c. 3.45x10^-3 s d. 100 s e. 1.73x10^-3 s
*December 6, 2013 by Shines*

**physics**

A parallel plate capacitor has square plates of side L= 12 cm and a distance d= 2 cm between the plates. Half of the capacitor areae is filled with a dielectric with k1 = 35. the other half is filled with a different dielectric with k2 = 8. The effective( equivalent ...
*November 22, 2011 by Jam*

**College Algebra**

Carbon-14 Dating. Only 10% of the carbon-14 in a samll wooden bowl remains. How old is the bowl? Half life of carbon is 5700 years.
*December 8, 2010 by Vince*

**Radioactivity or science**

A radioactive isotope source has a mass of 120ug. If the isotope had a half life of 20s, what would be the mass if the isotope after 2 mins?
*April 21, 2014 by Jannet*

**physics**

You drive on an interstae 10 from San Antonio to Huston, half the [b]time[/b] at 55km/h and the other half at 90km/h. On the way back you travel half the [b]distance[/b] at 55km/h and the other half at 90km/h. What is your average speed from San Antonio to Houston What is your...
*September 10, 2006 by ben*

**Chemistry**

You have 11.20 grams of compound. It is known that the compound has a half-life of 3.8 days. HOw long will it take for the compound to decay to 0.350 grams?
*December 2, 2011 by Missy*

**chemistry**

You have 11.20 grams of a compound. It is known that the compound has a half-life of 3.8 days. How long will it take for the compound to decay to 0.350 grams?
*December 5, 2011 by Anonymous*

**Math**

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay constant. (a) ...
*April 5, 2014 by Vanessa*

**Math**

A radioactive substance decays according to the formula Q(t) = Q0e−kt where Q(t) denotes the amount of the substance present at time t (measured in years), Q0 denotes the amount of the substance present initially, and k (a positive constant) is the decay constant. (a) ...
*April 6, 2014 by Vanessa*

**Radioactivity **

How are the terms "activity" and "becquerel" related? A radioactive isotope source has a mass of 120 g. If the isotope has a half life of 20 secs what would be the mass of the isotope in 2 mins?
*April 16, 2014 by Anonymous *

**Social Studies.\ASAP PLEASE**

What factors shaped the move from colonial, country life to modern, urban life? What was urban city life like during the rise of urbanization? How was it different or similar to modern urban life? Can you help me? I have not heard from my teacher about exactly what is need or ...
*April 7, 2010 by Maryanne*

**Chemistry**

a glavanic cell is set up by connecting the following half-cells together: nickle electrode in nickel nitrate solution and a copper electrode in copper nitrate solution. in which half-cell will oxidation occur? in which half-cell will reduction occur? write the half reaction ...
*July 19, 2009 by Cori*

**Math**

the average life expectancy in canada is 80.1 years. Estimate the country's life expectancy in hours? I know the answer is 700,800 but I cant for the life of me figure out how they get that! Thanks
*May 20, 2008 by Maggie*

**chem**

The half life of Am-241 is 432 y. If 2.00 g of Am-241 is present in a sample, what mass of Am-241 is present after 1000.0 y?
*September 19, 2014 by bekah*

**English**

If there were one thing that I’ve ever wanted to achieve in my life, it would be to become at least half the person she is. So I wrote this sentance but a lot of people say not to end with is. How can I rephrase it. Or is using is at the end of the sentance ok?
*February 3, 2009 by Lena*

**chemistry**

Rates of chemical reactions usually depend on temperature and pressure. However, half-life of all radioactive elements is independent of both T and p. How can these decay rates be independent of T if we beleive in the Arrhenius equation?
*July 27, 2010 by Jin*

**phyics**

Tritium (half-life = 12.3 y) is used to verify the age of expensive brandies. If an old brandy contains only the following fraction of the tritium present in new brandy, how long ago was it produced? 1/16
*September 17, 2010 by ashley*

**Chemistry**

N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
*November 29, 2012 by Odesa*

**chemistry**

N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
*November 29, 2012 by sveta*

**chemistry**

N2O5 dissolved in CCl4 decomposes to give N2O4 and O2. The reaction is first order with a half-life of 1234 seconds. How long will it take, in seconds, for the concentration of N2O5 to fall to 1.1% of its initial value?
*November 29, 2012 by NIK*

**chemistry/math**

100g of bone contain ratio of 14C and 12C. 6.8% 14C is present in the living tissue, how old was the skeleton? [for 14C, half-life is 5.73x10^3 years] please help me choose an equation for this type of question.
*October 15, 2008 by ronny*

**Chemistry**

A sample of sodium-24 with an activity of 12 mCi is used to study the rate of blow flow in the circulatory system. If sodium -24 has a half-life of 15 hours, what is the activity of the sodium after 2.5 d ?
*July 20, 2010 by Matt*

**Chemistry**

A 71 mg sample of a radioactive nuclide is administered to a patient to obtain an image of her thyroid. If the nuclide has a half-life of 12 hours, how much of the nuclide remains in the patient after 4.0 days?
*October 5, 2010 by Mr.Chemistry*

**university studies**

How have you used these actions to solve problems in your daily life? How are critical thinking skills in your daily life and in your academic life similar? How are they different?
*October 8, 2011 by us 101 week 9 DQ 3*

**SCIENCE**

IS THERE LIFE ON VENUS why dont you go find out? Probably there is life on Venus, but you have to be careful how you define life.
*August 18, 2005 by SEAN*

**math**

An artifact was found and tested for its carbon-14 content. If 76% of the original carbon-14 was still present, what is its probable age (to the nearest 100 years)? (Carbon-14 has a half-life of 5,730 years.)
*March 17, 2013 by buffy*

**math**

An artifact was found and tested for its carbon-14 content. If 79% of the original carbon-14 was still present, what is its probable age (to the nearest 100 years)? (Carbon-14 has a half-life of 5,730 years.)
*June 6, 2013 by ro*

**Algebra**

An artifact was found and tested for its carbon-14 content. If 74% of the orginal carbon-14 was still present, what is its probable age (to the nearest 100 years)? (Carbon-14 has a half life of 5730 years).
*May 5, 2014 by Kim Johnson*

**Alegbra**

An artifact was found and tested for its carbon-14 content. If 75% of the original carbon-14 was still present what is its probable age to the nearest 100 years?. carbon -14 has a half-life of 5,730 years.
*May 10, 2014 by Mary Ann*

**alegbra**

An artifact was found and tested for its carbon-14 content. If 75% of the original carbon-14 was still present, what is its probable age (to the nearest 100 years)? (Carbon-14 has a half-life of 5,730 years.) thank you
*May 11, 2014 by gary*

**Stats**

Suppose X & Y are two independent stocks' returns with: E(X) = E(Y) =15% and V(X) = 144, V(Y) = 256 Problem 1. Buy half X and half Y, so w1 = w2 = 0.5 and Z = (X+Y)/2 Note: The answer says that the variance is 100 but I thought it would be 200. Since I would be adding half ...
*September 14, 2012 by Matt*

**chemistry-balanced redox equations**

Use the following steps to balance the redox reaction below: Mg + Au+ Mg2+ + Au a. Write the oxidation and reduction half-reactions. Make sure each half-reaction is balanced for number of atoms and charge b. Multiply each half-reaction by the correct number, in order to ...
*March 25, 2012 by princess*

**chemistry**

1. If half cell A has a standard reduction potential of E= -1.10 V and half cell B has a standard reduction potential of E= 0.65 V, which half-cell is the anode? 2. Which half cell has the higher potential energy? 3. Calculate Ecell for this voltaic cell.
*July 14, 2012 by greentree*

**physics (mechanics)**

A running man has half the kinetic energy of a boy half his mass. The man speeds up by 1.30 m/s and then has the same kinetic energy as the boy. What is the speed (in meters/second) of the boy?
*April 12, 2012 by andrew*

**Half-Life**

Can someone please show me a detailed solution to this problem? Thanks. In a first order decompostion reaction, 42.6% of a compound decomposes in 18.5 minutes. How long, in minutes, will it take for only 25.0% of the compound to remain? The answer is: 46.2 (I just don't know ...
*June 21, 2009 by Critical*

**math**

The mass m(t) remaining after t days from a 70 g sample of thorium-234 is given by the equation shown below. m(t) = 70e-0.0274t Find the half-life of thorium-234. (Round your answer to the nearest tenth.)
*March 13, 2010 by Anonymous*

**chemistry**

Tritium (half-life = 12.3 y) is used to verify the age of expensive brandies. If an old brandy contains only the following fraction of the tritium present in new brandy, how long ago was it produced? 1/128
*September 16, 2010 by adrienne*

**chemistry**

N2O undergoes thermal decomposition at 730°C to nitrogen (N2) and oxygen (O2) via first-order kinetics with a half-life of 3.58 x 103 minutes. Calculate the time required for 90% of a sample of N2O to decompose at 730°C.
*December 5, 2011 by Cece*

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