Saturday

December 20, 2014

December 20, 2014

Number of results: 70,571

**chemistry**

The half-life of oxygen-15 is 124 s. If a sample of oxygen-15 has an activity of 4800 Bq, how many minutes will elapse before it has an activity of 600 Bq?
*September 27, 2014 by Anonymous*

**calculus**

The half-life of Radium-223 is 11.43 days. If a sample has a mass of 400 mg, find the mass (in mg) that remains after 6 days
*October 14, 2014 by w*

**Math**

The half life of Uranium 230 is 20.8 days. How long would it take for 20% of Uranium 230 to decay?
*January 11, 2009 by J*

**Exponential Decay**

the half-life of carbon-11 is 20 minutes. How long will it btake for 600g of carbon-11 to decay to 30g?
*October 22, 2009 by Mark*

**math**

39mg radioactive with 1/2 life is decay total in 2.5 years. How many mg it remain if half of the amount is decay in 2 years? Thank you!
*June 18, 2010 by Marie*

**Chemistry**

If the amount of raidoactive iodine-123 in a sample decreases from 0.4 to 0.1 g in 26.2 hours, what is the half-life of iodine-123?
*November 14, 2010 by Erin*

**Chemistry**

If the amount of radioactive iodine-123 in a sample decreases from 0.8 g to 0.1 g in 36.2 hours, what is the half-life of iodine-123
*April 17, 2011 by Sara*

**Science**

43Lb has a half life of 42 minutes. If you start with 100 grams, how many grams will you have after 84 minutes?
*January 28, 2014 by Sabrina*

**Physics**

At 08:00hrs a 2.7- m-long vertical stick in air casts a shadow 1.8 m long. If the same stick is placed at 08:00hrs in air in a flat bottomed pool of salt water half the height of the stick, how long is the shadow on the floor of the pool? (For this pool, n = 1.64.) I can't get...
*May 27, 2008 by Katie*

**Chemistry**

Ba-140 has a half life of 13.0 days. What fraction of a sample of Ba-140 will remain after 39 days? A. 1/8th B. 1/16th C. 1/2th D. 1/4th
*May 23, 2010 by Charleze*

**chemistry**

if you start with 100mg of radioactive material that has a half life of one hour, how many mg's of radioactive material would you have in 10.2284952 hours?
*February 1, 2011 by carlos*

**Chemistry**

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?
*February 12, 2012 by gary*

**Chemistry**

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?
*February 12, 2012 by gary*

**Chemistry**

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?
*February 12, 2012 by Steven*

**Chemistry**

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. How many beta particles are emitted in 190s by a 3.10mg sample of Co-60? What is the activity of the sample in Bq?
*February 13, 2012 by Steven*

**math**

only 5% of the carbon-14 in a small wooden bowl remains , how old is the bowl? Hint, half-life for carbon –14 us 5730 years
*April 4, 2012 by martha*

**chem**

the half life of oxygen-15 is 124 s. if a sample of oxygen-15 has an activity of 4000 Bq, how many minutes will elapse before it reaches an activity of 500Bq
*June 5, 2012 by Anonymous*

**chemistry**

a certain radioactive nuclide has a half life of 5.00 hour. Calcuate the decay rate for 1.000 mole of this nuclide __________ decay s-1
*July 12, 2012 by eric *

**College Algebra**

The half-life of a radioactive material is about 34.6 years. How much of a 1-gram sample of the material is left after 30 years?
*October 20, 2012 by Anonymous*

**Chemistry**

Calculate the time in which the activity of an element is reduced to 90% of its original value. The half-life period of the element is 1.4*10^10 years . Answer :- 2.13*10^9 years
*November 20, 2014 by Harsh*

**Science**

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value? Can anyone give me a VERY SIMPLE explanation of this please? Thank you.
*January 29, 2011 by Korina*

**chemistry**

If C14 has a half-life of 4,000 years, what fraction will be remaining after 36,000 years?
*July 7, 2011 by g*

**chemistry**

If there is a radiation that has a half life of 10 days and we have it for 110 days, what will be the fraction of radiation left?
*July 10, 2011 by g*

**Chemistry**

If there is a radiation that has a half life of 10 days and we have it for 110 days, what will be the fraction of radiation left?
*November 6, 2011 by Jennifer*

**help**

the half-life of a radium is 1690 years is 90 grams is present now, how much will be present in 70 years
*December 2, 2011 by Anonymous*

**CHEM**

An isotope has a half life of 56 days. It now has 10,000DPM/ml. What will its activity be 100 days from now?
*April 17, 2013 by Jared*

**Math**

half life of a drug in the bloodstream is 14 hours. By what factor does the concentration of the drug decrease in 22 hours?
*December 14, 2013 by Clare*

**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*

**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*

**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**

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*

**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*

**chemistry**

The half-life of I-131 is 8.00 days. If a medical treatment involves a dose of 400. mg of I-131, how much of the isotope remains after 48 days? 3.125 mg 6.25 mg 12.5 mg 25 mg
*December 2, 2014 by Tamera*

**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*

**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*

**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*

**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*

**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**

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*

**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!*

**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 *

**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*

**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.*

**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*

**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.*

**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*

**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*

**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- 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*

**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*

**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*

**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**

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*

**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*

**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**

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*

**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*

**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*

**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*

**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 *

**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*

**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*

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