Saturday

September 20, 2014

September 20, 2014

Number of results: 12,500

**math**

an extremely volatile substance, Ofnetite, has a half-life of 25 minutes. Find the percentage decrease of this substance in the first two hours.
*November 8, 2009 by katy*

**Chemistry 212**

the half life of F18 is 2.089x10^-4yrs. How long would it take (in days) for F18 to decrease to 78.71% of its initial amount?
*May 10, 2010 by pookie*

**Chemistry-help please!**

The half-life of Xe-133 is 126 hours. Starting with 250. mg, after 500 hours around how many mg remain? A. 63 B. 16 C. 32 D. 125
*May 23, 2010 by Charleze*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?
*February 24, 2011 by rachel*

**math**

Radioactive radium has a half-life of approximately 1599 years. What percent of a given amount remains after 100 years?
*February 24, 2011 by rachel*

**chemistry**

caffeine has a half-life of 4.6 hours in the human body.. How long would it take 125 milligrams tritium to decay to 22 milligrams?
*April 11, 2011 by cam*

**Chemistry **

carbon 14 has a half life of 5715 years. If you start with a 5 gram sample of 14C, what mass is left after 15,000 years?
*April 24, 2012 by Mima*

**Chemistry**

A fossil is found to have a C-14 level of 86% compared to living organisms. How old is the fossil?, (the half life of C14 is 5730 years).
*April 27, 2012 by Mima*

**Chemistry**

Carbon-14 has a half-life of 5730 years In a plant fossil you find that the 14 C has decayed to 1/8 of the original amount how long ago was this plant
*September 24, 2012 by Shay*

**Science chemistry**

It takes 1 hour and 17 min. for a 1.000gsample of a certain isotope to decay to 0.121g. What is the half-life of this isotope? plssss helpp
*September 24, 2012 by Shay*

**chemistry**

It takes 1 hour and 17 min. for a 1.000g sample of a certain isotope to decay to 0.121g. What is the half-life of this isotope? plssss helpp
*September 24, 2012 by Shay*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days
*November 29, 2012 by lan*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days
*November 29, 2012 by lan*

**earth science**

if carbon 14 has a half life of 24 days how much would be left of 220 gram sample after 168 days
*November 29, 2012 by lan*

**chemistry**

Carbon-14 has a half-life of 5730 . In a plant fossil, you find that the has decayed to 1/32.0 of the original amount. How long ago was this plant alive?
*December 3, 2012 by niles28*

**Science**

If a 20 gram sample of a radioactive substance has a half-life of 6000 years, how many grams would be present after 18000 years?
*December 5, 2012 by Owen*

**Biology**

The half-life of Carbon-14 is 5730 years. What is the age of a fossil containing 1/16 the amount of Carbon-14 of living organisms? Explain your calculation.
*December 9, 2012 by Melissa*

**UIW**

Neptunium-239 has a half-life of 2.35 days. How many days must elapse for a sample of 239Np to decay to 0.100% of its original quantity
*September 19, 2013 by Anonymous*

**chemistry**

use logic and simple math to determine how long it will take for a sample of potassium- 42 to decay from 8mg to 0.25mg if the half-life of this radioactive isotope is 124 hours
*October 12, 2010 by jay 1*

**College Chemistry**

How much time in years (assume a 365 day yr) would it take for a 1.6678g sample of 239Np to decay to a mass of 0.8671g if it has a half life of 2.030*10^5s
*May 5, 2011 by Jude*

**Chemistry**

Tc-99 is a radioactive isotope that decays by beta emission and is used by radiologists in the diagnosis of liver disease. Its decay behavior is shown by the activity-time table. What is its half-life?
*December 10, 2011 by Jennifer*

**Life of a Soldier**

Could you please give me some points, details explaining life of an average canadain soldier. Ive jotted down a few, but if you could give me some more, that would help me loads. Didn't get many hours of sleep Poor Living Conditions Had to stand out in the trenches daily, had ...
*October 12, 2011 by Anonymous*

**chemistry 2**

A voltaic cell is constructed with an Ag/Ag+ half-cell and a Pb/Pb2+ half-cell. Measurement shows that thesilver electrode is positive. -Write balanced half-reactions and the overall spontaneous reaction.
*April 27, 2012 by anonymous*

**physics**

A baseball leaves a pitcher's hand horizontally at a speed of 115 km/h. The distance to the batter is 18.3 m. (Ignore the effect of air resistance.) (a) How long does the ball take to travel the first half of that distance? (b) The second half? (c) How far does the ball fall ...
*October 7, 2012 by tatiana*

**physics**

A baseball leaves a pitcher's hand horizontally at a speed of 115 km/h. The distance to the batter is 18.3 m. (Ignore the effect of air resistance.) (a) How long does the ball take to travel the first half of that distance? (b) The second half? (c) How far does the ball fall ...
*September 19, 2013 by kristy*

**Physics**

A certian radioactive isotope has a half-life of 1 hour. If you start with 1 gram of the material at noon, how much of the original isotope will the sample contain at 3 pm? At 6 pm? At 10 pm?
*November 17, 2007 by Judy*

**math**

if the rate for radioactive decay for a substance is r=-.0063 and time is being measured in days how do you find the half-life of the substance to the nearest hour?
*March 30, 2009 by mike*

**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?
*December 21, 2010 by Bree*

**math**

how to compute this problem? a certain element has a half life of 12 years. if there were 1000 milligrams originally, find the remaining amount after 20 years?
*January 12, 2011 by diane*

**chemistry**

the mass of cobalt-60 in a sample is found to have decreased from 0.800g to 0.200g in a period of 10.5 years. from this info calculate the half-life of cobalt-60
*April 6, 2011 by shaleena*

**chemistry**

the mass of cobalt-60 in a sample is found to have decreased from 0.800g to 0.200g in a period of 10.5 years. from this info calculate the half-life of cobalt-60
*April 6, 2011 by shaleena*

**chemistry**

a sample of a radioisotope had a mass of 100.0 grams. After exactly 24 days, 6.25 grams remained. The half life of the isotope is _________
*June 3, 2011 by rick*

**chem**

Cobalt-60, which undergoes beta decay, has a half-life of 5.26 yr. (a) How many beta particles are emitted in 47.0 s by a 2.39-mg sample of 60Co? i got 2.44e19 but thast wrong
*September 12, 2012 by sara*

**math**

3. The half-life of a certain drug in the human body is 8 hours how long it would take for a dose of this drug to decay to 0.1% of its initial level?
*November 12, 2013 by hannah*

**math**

Show that if a radioactive substance has a half life of T, then the corresponding constant k in the exponential decay function is given by k=-ln(2)/T I'm confused about how to show that that is true.
*September 4, 2014 by lucy*

**Alg2**

Radioactive iodine is used to determine the health of the thyroid gland. It decays according to the equation y=ae -0.0856t where t is in days. Find the half-life of this substance. Round to the tenths place.
*December 6, 2011 by Rock*

**Alg2**

Radioactive iodine is used to determine the health of the thyroid gland. It decays according to the equation y=ae -0.0856t where t is in days. Find the half-life of this substance. Round to the tenths place.
*December 8, 2011 by Rock*

**Physics**

Determine the activity of 1.11 g of 88Ra226 (a) in disintegrations per second (Bq) (b) and in Curies (Ci). The half-life is 1600 yr (1 yr = 3.156 x 10^7 s). 1 Ci is equal to 3.7 x 10^10 Bq. I keep getting the wrong answer and use the equation H=kNo
*July 29, 2012 by Beth*

**Chemistry**

In solution, hypochlorite ion is known to decompose with a second-order rate law. If [ClO-]0 = 0.0570 M and k = 2.06x10-4 M-1·min-1, calculate the half-life for this reaction 2ClO- 2Cl- + O2.
*September 6, 2012 by Amber*

**chemistry math**

linen scrolls contain 80.9% of Carbon-14. how old are the scrolls if the half-life for deacy is 5.73X10^3?? plz tell me what type of equation to use.
*October 15, 2008 by ronny*

**Calculus**

A certain radioactive material decays exponetially. The percent, P, of the material left after t years is given by P(t)= 100(1.2)^-t a)Determine the half life of the substance
*April 13, 2010 by lala*

**chemistry**

Consider the first order reaction A --> products where 25% of A disappears in 24 seconds. What is the half life of this reaction? ...i thought it would just be doubled but it isn't. i'd appreciate an explanation.
*April 29, 2010 by omar*

**Alg2**

A piece of wood discovered in an archaeological dig was found to have lost 62% of it's carbon-14. Carbon-14 has a half-life of 5630 years. Determine it's age.
*June 1, 2010 by Cal*

**Calculus **

Radius decays at a rate of that is proportional to its mass, and has a half-life of 1590 years. If 20 g of radium is present initially, how long will it take for 90% of this mass to decay?
*June 17, 2010 by Anonymous*

**Math**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed? ? yr
*July 15, 2011 by Lee Ann*

**algebra**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed
*July 18, 2011 by sissy*

**algebra**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 20, 2011 by Anonymous*

**math**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.4% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*October 22, 2011 by lady*

**algebra**

The half-life of plutonium-234 is 9 hours. If 40 milligrams is present now, how much will be present in 4 days? (Round your answer to three decimal places.)
*November 20, 2011 by meghan*

**algebra**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.4% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*December 16, 2011 by lance*

**math**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.3% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*January 22, 2012 by Anonymous*

**algebra**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*January 28, 2012 by Anonymous*

**College algebra**

The radioactive element has a half-life of about 28 years and sometimes contaminates the soil. After 47 years, what percentage of a sample of the elements remain?
*May 12, 2013 by Taylor*

**Chemistry 2**

For the fist order reaction A <-> B, calculate the t1/2(half life) and k(rate constant) and also fill in the blanks. A-Concetration t-time 20 0 10 ? 5 40 sec 3 ? ? 500 sec t1/2=? k=?
*March 3, 2014 by Ivan *

**Chemistry 2**

For the fist order reaction A <-> B, calculate the t1/2(half life) and k(rate constant) and also fill in the blanks. A-Concetration t-time 20 0 10 ? 5 40 sec 3 ? ? 500 sec t1/2=? k=?
*March 3, 2014 by Ivan *

**mechanics**

The change in length of a steel wire under an applied load can be halved by keeping all other conditions constant but using: A. a different material having a Young's modulus half that of steel B half the cross sectional area of the steel wire C half the length of steel wire D ...
*February 24, 2013 by dmkp*

**College Math**

A certain man spent 10% of his life in childhood and 20% of his life as a young adult at which time he married his lovely bride. Five years later his son was born. His son lived to be half the age of his father when his father died. The man died ten years after his son died. ...
*September 29, 2008 by Jess*

**Chemistry **

If 100.0 g of carbon-14 decays until only 25.0 g of carbon is left after 11,460 y, what is the half-life of carbon-14?
*December 11, 2012 by Jacob *

**Chemistry**

I don't know the correct answer thats what i have to find. for the first part here is my work..... 6.2e-4/min=0.0372seconds half life: t_1/2=0.693/0.372s =18.6sec*1min/60sec=0.310min (which is not right!)
*November 10, 2009 by Dena*

**Chemistry**

The half-life for the first-order conversion of A to B is 56.5 hours. How long does it take for the concentration of A to decrease to 10.0% of its original amount? Our professor has given us the answer - 188hr but I am not entirely sure how he got it.
*February 23, 2014 by Kristen*

**chemistry**

A 7.500-mg sample of chromium-55 is analyzed after 14.0 min. and found to contain 0.469 mg of chromium-55. what is the half-life of chromium-55?
*November 2, 2008 by Jasmine08*

**chemistry **

a 7.500-mg sample of chromium-55 is analyzed after 14.0 min and found to contain 0.469 mg of chromium-55. what is the half-life of chromium-55
*February 8, 2012 by lisa*

**math**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 97.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 17, 2011 by Anonymous*

**math**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 97.4% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 26, 2011 by Anonymous*

**algebra**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.8% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 27, 2011 by Anonymous*

**algebra**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.8% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 27, 2011 by Anonymous*

**algebra**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.6% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 27, 2011 by Anonymous*

**math**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.7% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed? yr
*October 20, 2011 by Anonymous*

**uncc**

the half-life of 234U, uranium-234, is 2.52 x 10^5yr. If 98.5% of thee uranium in the original sample is present, what length of time (to the nearest thousand years) has elasped
*October 25, 2011 by ellen*

**pre algebra**

The half-life of 234U, uranium-234, is 2.52 105 yr. If 98.6% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*April 29, 2012 by Anonymous*

**ALGEBRA**

The half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.3% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed? =
*June 14, 2012 by Urgen please help*

**Physical Science- Help Please!**

Suppose that you are given a 100 gram sample of a radioactive substance with a half-life of 32 days. How many grams will be left after 192 days?
*December 5, 2012 by Molly*

**MATH104**

he half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 97.5% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed? yr
*December 18, 2012 by ABDALLA*

**chemistry**

Strontium-90 decays through the emission of beta particles. It has a half-life of 29 years. How long does it take for 80% of a sample of strontium-90 to decay? Show process of how you got this
*January 10, 2013 by Urgent Help*

**college algebra**

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 17, 2013 by Dee*

**math**

half of a gallon is a half gallon. half of a half gallon is a quart. half of a quart is a pint. half of a pint is a cup. a cup is what fraction of a quart? Is the answer 1/4?
*February 27, 2011 by Trevor*

**mechanics of materials**

The change in length of a steel wire under an applied load can be halved by keeping all other conditions constant but using:which of the following is correct A. a different material having a Young's modulus half that of steel B half the cross sectional area of the steel wire C...
*February 22, 2013 by dmkp*

**adult education**

How will your life experiences prove beneficial as you move through your degree program? Briefly describe two life experiences and illustrate how each will be useful as you pursue academic goals. How can you reject the negative influences in your life and benefit from the ...
*November 7, 2010 by tee*

**chemistry**

You have a compound that is subject to decay. If you originally started with 80 g of the compound and you ended up with 5 grams 30 days later, what is the half-life of the compound?
*December 5, 2011 by Anonymous*

**maths lit, geography, life science, history, life orientation, english, tswana**

what can I do with my life with all this subjects that I studied?.
*July 18, 2014 by Ernest Mmutlana*

**mechanics of materials**

Select the correct answer.The change in length of a steel wire under an applied load can be halved by keeping all other conditions constant but using: A. A different material having a Young's modulus half that of steel B half the cross sectional area of the steel wire C half ...
*February 21, 2013 by dmkp*

**shakespeare**

places in his life can it be where he was born what else conflicts in his life idk women in his life anne hathaway his wife men in his life can it be his fayher and the ppl he owrked with and his publisher children in his life susanna hamnet and judith mistakes he made idk ...
*April 22, 2014 by Reina B.*

**math**

If a hen and a half lay an egg and a half in a day and a half, how many hens are needed to lay a dozen eggs in one day?
*November 28, 2007 by New Girl 102*

**chemistry**

follows first-order kinetics and has an activation energy of 244 kJ mol-1. At 684 K, k = 0.00000508 s-1. What is the half-life (min) for this reaction at 427 °C ? Round your answer to 3 significant figures. I really dont know what to do
*November 19, 2010 by bobjahng2*

**Calculus**

Skeletal remains had lost 81% of the C-14 they originally contained. Determine the approximate age of the bones. (Assume the half life of carbon-14 is 5730 years. Round your answer to the nearest whole number.) yr
*July 12, 2013 by Anonymous*

**calculus**

Skeletal remains had lost 70% of the C-14 they originally contained. Determine the approximate age of the bones. (Assume the half life of carbon-14 is 5730 years. Round your answer to the nearest whole number.)
*March 2, 2014 by angie*

**Math**

Skeletal remains had lost 84% of the C-14 they originally contained. Determine the approximate age of the bones. (Assume the half life of carbon-14 is 5730 years. Round your answer to the nearest whole number.)
*April 5, 2014 by Vanessa*

**History**

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?
*January 4, 2010 by ggift*

**Chemistry**

I need help with the following problem: A fabric remnant from a burial site had a 14 C:12 C ratio of 0.838 of the original value. How old is the fabric? (half-life of 14 C = 5370 years)
*April 29, 2009 by Sophie*

**math**

How long will it take a given quantity of carbon-14 to lose 99.9% of its radioactivity if the half life is 5730 years? The formula I have been given is Q=ae^rt This is using log and ln functions.
*April 25, 2011 by Niki*

**Algebra 2**

A 14 gram sample of a substance that's used to preserve fruit and vegetables has a k-value of 0.1092. Find the substance's half-life, in days. Round your answer to the nearest tenth.
*May 7, 2013 by Tristan*

**chemistry**

Use the following steps to balance the redox reaction below: Mg + Au+ Mg2+ + Au -Write the oxidation and reduction half-reactions. Make sure each half-reaction is balanced for number of atoms and charge. -Multiply each half-reaction by the correct number, in order to balance ...
*February 8, 2012 by Adrian*

**Chemistry**

a compound decomposes with half life of 8seconds and is independent of concentration.how much time is consumed to convert the concentration of one sixteenth of its initial concentration?
*October 23, 2012 by Maria *

**Chemistry 2**

For a second order reaction A <--> B, calculate the t1/2 (half life) and the k(constant) and also fill in the blanks. A (concentration) t(time) 20 0 sec 10 ? 5 40 sec 3 ? ? 200 sec t1/2=? k=?
*March 3, 2014 by Ivan *

**Ethics**

Which of the following answers to the meaning of life did Tolstoy hold prior to his change of heart and mind? my answer is A a. Life has no meaning, and we must embrace that fact. b. Life's meaning is to provide comfort for oneself and one's family. c. Life's meaning is to ...
*February 18, 2014 by Annmarie*

**physics**

Suppose 32000 radioactive nuclei are in a sample. About how many remain after two days if the half-life is 22 hrs? What is the initial activity of the sample in decays per minute?
*May 5, 2009 by Anonymous*

**chemistry**

use the nuclear decay equation to find out how much a 7mg sample of iodine 128 remains after 116 minutes if the half life of this isotope is 25 minutes.
*October 12, 2010 by dela*

**science**

12. Aluminum in blood plasma was shown to undergo a first order elimination reaction with a half-life of 160 days. If the initial concentration was 8.2 µg/L, how long will it take for the concentration to drop to 2.5 µg/L?
*February 13, 2011 by dan*

**math**

solve the problem. the half-life of 234U, uranium-234, is 2.52 multiplied by 105 yr. If 98.3% of the uranium in the original sample is present, what length of time (to the nearest thousand years) has elapsed?
*July 26, 2011 by juliet*

**Chem**

Radioactive 24Na with a half-life of 14.8 hours is injected into an animal in a tracer experiment. How many hours will it take for the radioactivity to fall to 12.5% of its original intensity? I am confused on what number to start with
*August 27, 2013 by Colby*

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