Tuesday

July 22, 2014

July 22, 2014

Number of results: 10,257

**calculus**

A sample of a radioactive substance decayed to 94.5% of its original amount after a year. (Round your answers to two decimal places.) (a) What is the half-life of the substance? (b) How long would it take the sample to decay to 65% of its original amount?
*November 9, 2012 by kela*

**Calc**

A sample of a radioactive substance decayed to 93.5% of its original amount after a year. a) What is the half-life of the substance? ? years (b) How long would it take the sample to decay to 10% of its original amount? ? years
*November 8, 2009 by Lee*

**Science**

Radioactive substance decays so that after t years, the amount remaining, expressed as a percent of the original amount, is A(t)=100(1.6)^(-t). a) Determine the function A’, which represent the rate of decay of the substance. b) what is the half-life for this substance? c) ...
*March 6, 2012 by jessica*

**MATH!**

The mass of a radioactive substance follows an exponential decay model, with a decay rate of 5% per day. A sample of this radioactive substance was taken six days ago. If the sample has a mass of 3 kg today, find the initial mass of the sample. Round your answer to two decimal...
*March 15, 2012 by Kim*

**calculus**

The rate at which an amount of a radioactive substance decays is modeled by the differential equation dA/dt = kA, where A is the mass in grams, t is the time in years, and k is a constant. Answer the following. a) If a 100-gram sample of the radioactive substance decays to 95 ...
*March 19, 2012 by ronnieday*

**science**

A 10g sample of radioactive substances is lift to decay for five half-lives. How much of the radioactive substance remains?
*February 19, 2013 by mirian hernandez*

**calculus**

Carbon-14 is a radioactive substance produced in the Earth's atmosphere and then absorbed by plants and animals on the surface of the earth. It has a half-life (the time it takes for half the amount of a sample to decay) of approximately 5730 years. Using this known piece of ...
*July 24, 2009 by j*

**precal**

If the half-life of a certain radioactive substance is 2000 years, estimate how many years must elapse before only 35% of the radioactive substance remains?
*January 22, 2013 by james*

**Math-Exponential Decay**

A lab technician had 58 grams of a radioactive substance. Ten days later, only 52 grams remained. Find the half-life of the radioactive substance.
*May 12, 2014 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*

**Science- Radioactive Dating**

Which of the following statements about radioactive dating is true? a. Radioactive decay is the rate at which new atoms form. b. During radioactive decay, atoms break down, releasing particles or energy. c. The rate of decay of a radioactive element cannot be approximated. d. ...
*October 10, 2013 by Anonymous*

**algebra**

Julie has 250 grams of a radioactive substance. The substance decays every hour. How long will it take until she has 20 grams of the substance left?
*September 9, 2013 by Sozy *

**Chemistry**

How many half lives will it take for a sample of a radioactive isotope containing 20000 radioactive nuclei to decay to 2000 radioactive nuclei
*November 16, 2010 by Dianne*

**Calculus-derivatives**

Verify if these are correct answers. 1. The derivative of f(x)=e^2x -e^-2x is f'(x)=2e^2x - 2e^-2x? 2.A certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, given by the function f(x)=3e^-3t. What is the rate of...
*March 6, 2012 by Matthew*

**Physics**

A radioactive substance decays from 2.0kg to 1.6kg in 156 days. What is the decay constant and the half life of the substance?
*August 6, 2013 by Alice*

**math30**

The mass of a radioactive sample is represented in the graph below. The initial mass of 32 mg decays to 8 mg after 21 hours. 1)What is the half-life of the radioactive sample, in minutes? 2)Solve each equation. a. 4 8x-1 = 8 b. 3^(2x-5) = 1/27x
*July 3, 2012 by alejandro*

**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*

**Chemistry**

A radioactive sample contains 3.25 1018 atoms of a nuclide that decays at a rate of 3.4 1013 disintegrations per 26 min. (a) What percentage of the nuclide will have decayed after 159 d? % (b) How many atoms of the nuclide will remain in the sample? atoms (c) What is the half-...
*April 16, 2010 by Trixie T*

**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*

**chemistry**

If you accidentally spill phosphorus-32 onto your shoe, how long would it take before 99.9 of the radioactive material has decayed so that you can safely wear the shoes again?
*May 12, 2011 by brittany*

**Calculus-Modeling Equations**

An unknown radioactive element decays into non-radioactive substances. In 420 days the radioactivity of a sample decreases by 39 percent. 1.What is the half-life of the element? 2.How long will it take for a sample of 100 mg to decay to 46 mg?
*March 6, 2009 by Kim*

**queen of peace academy**

If 1g of sodium-24 has decayed from a sample that was orinally 2g. How old is the sample?
*March 28, 2013 by michael*

**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*

**chm**

An unknown radioactive substance has a half-life of 3.20 . If 34.8 of the substance is currently present, what mass was present 8.00 hours ago?
*February 10, 2012 by cp*

**precalculus**

Twenty percent of a radioactive substance decays in ten years. By what percent does the substance decay each year?
*March 3, 2011 by katrina*

**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*

**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*

**AP Chem**

Help with these two please. 105. A radioactive metal atom decays (goes to another kind of atom) by emitting an alpha particle (He+2 ion). The alpha particles are collected as helium gas. A sample of helium with a volume of 12.05 mL was obtained at 765 mmHg and 23 Degrees C. ...
*November 12, 2008 by Anna*

**chemistry**

A particular radioactive substance has a half-life of 4 minutes. How long will it take for 250 g of this radioactive material to decay to less than 0.1g? 24 min 36 min 40 min 48 min 72 min I got 32 min but that not one of the choices. Please help
*December 5, 2011 by Anonymous*

**Calculus**

The quantity Q of radioactive carbon remaining in a 200-gram wood sample at time t is given by the expression Q(t)=200e^(−0.000225⋅t). How much radioactive carbon remains in the sample after 100500 years? I just plugged in 100500 as t and got 3.02375 grams as an ...
*May 17, 2014 by Ann*

**Physics**

Suppose a hypothetical radioactive nucleus (Hy) has a half-life of 10 days. If we have 80 gms of the substance at the start of an experiment, how many gms of the substance will remain undecayed after 30 days
*May 10, 2008 by Tim*

**math**

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element? half-life: b)How long will it take for a sample of 100 mg to decay to 51 mg? time needed:
*May 18, 2013 by Rachel*

**chemistry**

A radioactive sample contains 3.25 1018 atoms of a nuclide that decays at a rate of 3.4 1013 disintegrations per 26 min. (a) What percentage of the nuclide will have decayed after 159 d? % (b) How many atoms of the nuclide will remain in the sample? atoms (c) What is the half-...
*April 16, 2010 by Trixie *

**Chemistry**

If a 100.0 gram sample of a radioactive isotope goes through three half-lives, how much of the original radioactive isotope will remain?
*January 24, 2013 by OhSnap*

**Pam**

A 56.59 g sample of a substance is initially at 20.5 °C. After absorbing 1267 J of heat, the temperature of the substance is 116.5 °C. What is the specific heat (c) of the substance?
*December 5, 2013 by Chemistry*

**chemistry**

what is the density of an 84.7g sample of an unknown substance if the sample occupies 49.6cm3? what volume would be occupied by 7.75g of this same substance? PLEASE help need the answer tonight i have a test tomorrow i kind of not understand the second question. THANK YOU SO ...
*September 22, 2010 by heather*

**Chemistry**

Assume that a reaction occurs in which unknown substances R and S react to form unknown substances T and U. From the information below, determine the mass of substance T that will be formed if 45.0 grams of substance R reacts with 23.0 grams of substance S. (Assume that the ...
*May 20, 2008 by Daniel*

**Chemistry**

The half-life of phosphorus-32 is 14.26 days. The decay constant is k=4.86×10−2/days. If you accidentally spill phosphorus-32 onto your shoe, how long would it take before 99.9% of the radioactive material has decayed so that you can safely wear the shoes again?
*May 1, 2011 by Anonymous*

**Chemistry**

Q1. The blood volume in a cancer patient was measured by injecting 5.0 mL of Na2SO4(aq) labeled with 35S (t1/2 = 87.4 d). The activity of the sample was 300 µCi. After 22 min, 12.9 mL of blood was withdrawn from the man and the activity of that sample was found to be 0.75 µCi...
*April 16, 2010 by Trixie *

**chemistry**

sometimes,instead of percentage composition, you will have the composition of a mass sample. using the actual mass of the sample, determine the empirical formula for compounds that have the following analyses. b. a 13.07g sample of an unknown substance is composed of 9.48g of ...
*February 23, 2013 by tula*

**Chemistry please check**

1. All of the naturally occurring radioactive decay series end when the radioactive elements have decayed to bismuth (Bi) hydrogen (H) lead (Pb) uranium (U) answer: Uranium (U) 2. This type of radiation can easily pass through a human. gamma ultra-violet beta alpha answer: ...
*February 15, 2008 by Mary*

**Science**

If the half-life of a radionuclide is 1 month, is a sample of it completely decayed after 2 months?
*March 22, 2013 by Dee*

**chemistry**

Substance A has a specific heat of .650J/gK and substance B has a specific heat of .325J/gK. If 100 J of energy is applied to a 10 g sample of each substance, which will have a higher temperature?
*September 19, 2011 by Anonymous*

**chemistry**

Substance A has a specific heat of .650J/gK and substance B has a specific heat of .325J/gK. If 100 J of energy is applied to a 10 g sample of each substance, which will have a higher temperature?
*September 19, 2011 by Anonymous*

**chemistry**

Which of the following is true of a substance with a pH of 11.0? A. The substance is an acid. B. The substance is a base. C. The substance is neutral. D. The substance is a transition metal. I think A
*November 10, 2012 by Keri*

**chemistry**

what is the density of a substance if a 2.50 ml sample has a mass of 0.880g at room temperature? what is the specific gravity of the substance?
*September 9, 2012 by Sasha nelson*

**Physcis 30**

Q1) If there are 100 radioactive atoms with a half-life of 30 seconds, how many radioactive atoms will remain after one half-life (30 seconds)? How many will remain after two half-lives (60 seconds)? Three half-lives? So basically, after 30 seconds it will be 50.After 60 sec. ...
*January 6, 2011 by Marium*

**Calculus**

The half life of a certain radioactive substance is 10 years. How long will it take for 18 gms of the substance to decay to 6 gms? A. 6 ln 10 years B. 10 ln 6 years C. 10 (ln 3)/(ln 6) years D. 18 ln 10 years E. 10 (ln 3)/(ln 2) years
*January 27, 2013 by Anonymous*

**Science Lab -Half-Life of Popcorn**

When a radioactive sample decays, there is one less parent nuclei and one more daughter nuclei. As this decay process continues, the number parent nuclei decreases and the number of daughter nuclei increases. Eventually there are no parent nuclei increases. Eventually there ...
*October 29, 2010 by Anonymous*

**Physics**

100-g sample of substance is heated to 100˚C and placed into calorimeter cup containing 150 g of water at 25˚C. The sample raises the temperature of water to 32.1. What is the specific heat of the substance?
*March 21, 2010 by John*

**physics/science**

i dont understand why radioactive waste is stored underground is it because it is a harmful substance
*April 10, 2008 by exam in 3 weeks*

**Science**

What fraction of the original activity of a radioactive substance will remain at the end of half-life?
*July 16, 2012 by Nezz*

**chemistry**

a radioactive material is undergoing nuclear decay. After 40 minutes, 25% of the sample remains. What is the half-life of the sample
*August 27, 2011 by marjani*

**advanced functions HELP!!!**

Radioactive decay is the process by which an unstable element transforms into different element, typically releasing energy as it does so. For 500g of a radioactive substance with a half-life of 5.2 hours, the amount remaining is given by the formula M(t)=500(0.5) ^ t/5.2 a) ...
*December 10, 2008 by james*

**8th Grade Earth Science Help?**

Which of the following terms refers to the time it takes for one-half of the radioactive atoms in a sample of a radioactive element to decay? - relative age - absolute age - potassium-argon data - half-life** Is my answer correct?
*January 14, 2014 by Rainshine*

**Science**

A material has 32 atoms in all; 24 decayed and the rest undecayed. If the half-life of the radioactive material is 1000 years, what is the age of the material? a. 1000 years b. 2000 years c. 3000 years d. 4000 years
*April 15, 2009 by Angie*

**Chemistry**

How much a 2.00 g 239 Pu would have decayed after 1.6 x 10^4 years? The half-life for 239 Pu is 2.4 x 10^4 years. amount remaining= originalamount*(.5)^(1.6/2.4) amount decayed = original - amountremaining
*November 26, 2006 by James*

**science **

The half-life of carbon 14 is 5730 years. if a 1 g sample of old carbon is 1/8 as radioactive as 1 g of a current sample, then the age of the old sample is about ___________years. 22,900 17,200 11,500 716
*March 5, 2012 by chuck *

**Pre Calculus**

Exponential Growth and Decay Find the half-life of a radioactive substance that decays by 5% in 9 years.
*October 22, 2011 by Josh*

**math**

A researchr assistant made 160mg of a radioactive, and found that there was only 20mg left after 45hours. a) What is the half-life of this substance? b) Write a function to represent the amount of substance left after x hours c) If the researcher kew he needed 100mg of the ...
*June 23, 2013 by Kristen*

**chemistry**

Substance A and substance B react to form substance C as described by the equation: A + B ↔ C If only substance A and substance B are placed in an enclosed vessel and allowed to react what would the reaction be?
*June 13, 2011 by guilford technical college*

**Chemistry**

How do you calculate the amount of a radioactive substance remaining after an integral number of half-lifes have passed?
*April 6, 2010 by Tristan*

**Physics**

A radioactive substance decays from 2.0kg to 1.6kg in 156 days. How long would it take to decay to 1.1kg?
*August 7, 2013 by Alice*

**Chemistry**

Suppose 1.0 mol of substance A reacts with 1.0 mol of substance B. to produce 2.0 mol of substance C. In a reaction, 2.4 mol of substance A is allowed to react with 2.1 mol of substance B. What amount in moles of substance c is produced?
*April 1, 2009 by Andrew*

**PLS HELP ASAP 1 SUPER HARD & ANNOYING QUESTION**

Use the diagram to answer question 13. so substance A looks like a row of three little circles on the top and bottom all organized (total six dots). substance b is all clumped together circles and is disorganized. 13. How can substance A and B be compared? Choose all that ...
*March 12, 2014 by sonamy4eva*

**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**

Sometimes, instead of percentages compostion, you will have the composition of a sample by mass. Using the actual mass of the sample, determine the empirical formula for compounds that have the following analyses. A. a .858g sample of an unkown substance is composed of .537g ...
*January 24, 2009 by Chopsticks*

**physical science**

A certain radioactive substance has a half-life of 1 hour. If you start with 1 gram of the material at noon, how much will be left at 3:00 P.M.? At 6:00 P.M.? At 10:00 P.M.?
*November 2, 2011 by cheryl*

**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**

An unknown substance has a mass of 17.3 . When the substance absorbs 1.557×102 of heat, the temperature of the substance is raised from 25.0 to 45.0 . What is the most likely identity of the substance?
*September 20, 2010 by Kyle*

**chemistry**

A certain substance has a molar heat of vaporization of 54.2 kJ/mol. How much of the substance is in a sample that requires 80.0 kJ to vaporize? Answer in units of mol
*March 1, 2012 by anonymous *

**physics**

The half life of a radioactive sample is 6.93 days.after how many days will only one -tenth of the sample be left behind?
*August 1, 2012 by Mira*

**Science (urgent)**

Suppose 13.7kJ of heat are removed from 33.5g liquid sample of ethanol at 26.8^oC. When all this heatis removed from the substance, at what temperature and in what states will you find the substance?
*May 4, 2009 by Nick*

**chemisrty**

When a substance changes from one phase to another, which of the following occurs? the substance loses or gains heat the average kenetic energy of the substance changes the temperature of a substance changes the molecular motion of a substance changes
*November 16, 2012 by Tasia*

**Math**

Find the half-life (in hours) of a radioactive substance that is reduced by 10 percent in 5 hours.
*August 28, 2012 by David *

**math**

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physics. You purify a sample of 2 grams. One of your colleagues steals half of it, and eight days later you find that 0.1 gram of the radioactive material is ...
*October 21, 2012 by Roseanne*

**Physical Science**

a student is given a 10 gram sample of gold that has a density of 19.32g/cm3. The student is then given a 5 gram sample of an unknown substance and told the density of the unknown substance is 19.32g/cm3. What is the unknown substance
*September 10, 2013 by Tyler*

**Chemistry**

A 50.6 mg sample of sodium perchlorate contains radioactive chlorine-36 (whose atomic mass is 36.0 amu). If 29.6% of the chlorine atoms in the sample are chlorine-36 and the remainder is naturally occurring nonradioactive chlorine atoms, how many disintegrations per second are...
*February 13, 2012 by Steven*

**Physics**

A radioactive substance decays from 2.0kg to 1.6kg in 156 days. How much will be left after 201 days?
*August 7, 2013 by Alice*

**11th grade**

what is the density of an 84.7g sample of an unknown substance if the sample occupies 49.6cm3
*September 9, 2009 by Anonymous*

**Chemistry-pH**

If you are given a colored substance as a sample, how would you measure the pH of a sample?
*January 25, 2011 by Bam*

**math**

The decay of 333 mg of a radioactive substance is given by A(t) = 333e-0.024t, where t is time in years. Find the amount left after 17 years.
*April 8, 2011 by allison*

**science HElp **

Ph scale Which on is true A substance with ph is twice as acidic as substance with ph of 4. A subtances with ph 3 is 10 as acidic as substance with ph of 4. A substance with ph 3 twice as alkies as substances with ph 4. a substancs with ph 3 10 time alkies as substance with ph...
*November 23, 2011 by shan*

** Chem**

A radioactive isotope sample has a hal
*December 6, 2013 by Lulu*

**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*

**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*

**Physics**

Consider a radioactive sample with a half-life of one week. How much of the original sample will be left at the end of the second week? The third week? The fourth week?
*August 29, 2013 by Tracee*

**chemistry**

The half-life for the radioactive decay of calcium-47 is 4.5 days.If a sample has an activity of 4.00uCi after 13.5 days, what was the initial activity of the sample?
*September 26, 2012 by Shay*

**chemistry -- radioactive decay **

suppose you have a 150 gram sample of radioactive decay god-191 which has a half- life of 3.4 hours. how many grams of gold will ramain after 10hrs ? after 24 hrs? answer : 10 hrs :10/3.4= 2.94 times 150*(1/2)^2.94 = 18.75 grams 24 hrs: 24/3.4 = 7.06 150*(1/2)^7.06= 1.12 right...
*September 18, 2012 by Maria*

**chemistry**

2. Imagine you have two beakers. Both beakers are filled with the same amount of water. The water in both beakers is the same temperature as well. You add 50 g of Substance A to the first beaker, and 50 g of Substance B to the second beaker. After stirring both beakers, there ...
*October 22, 2009 by fatima*

**chemistry**

How long will it take for 25% of the C-14 atoms in a sample of C-14 to decay? The half-life for the radioactive decay of C-14 is 5730 years. If a sample of C-14 initially contains 1.1 mmol of C-14 , how many millimoles will be left after 2275 years?
*February 28, 2010 by Anonymous*

**chemistry**

An unknown substance has a mass of 28.1 g. The temperature of the substance increases by 16.3 degrees Celsius when 176 J of heat is added to the substance. What is the most likely identity of the substance? The table lists the specific heat capacities of select substances.
*January 26, 2014 by bob*

**college physics**

A 215 g sample of a substance is heated to 330 degrees C and then plunged into a 105 g aluminum calorimeter cup containing 165 g of water and a 17 g glass thermometer at 12.5 degrees C. The final temp is 35.0 degrees C. What is the specific heat of the substance?
*May 6, 2010 by E*

**Chemistry**

The figure below is a heat curve for an unknown outerspace substance discovered by the Mars rover. By understanding the heat curve, scientists can make inferences about the composition of the planet. What is the temperature of fusion, Tfusion, and vaporization, Tvapor, for ...
*December 9, 2012 by Anon*

**chemistry**

If you have 12 moles of a substance, how many molecules do you have of that substance? Suppose the substance has a molecular weight of 342. How many grams of that substance would you have to dissolve in a liter of water to make a 12 M solution?
*September 3, 2011 by VANESSA*

**chemistry**

a radioactive material is undergoin nuclear decay. After 40 minutes, 25% of the sample remains. What is the half life of the sample? Pls say the formula how to calculate it a)10 mins b) 20 mins c) 40 mins d)80 mins e) 160 mins
*May 28, 2012 by star*

**Chemistry**

Caffeine C8H10N4O2, is a stimulant found in a tea and coffee. A sample of the substance was dissolved in 45.0g of choloroform CHCl3 to give a 0.0946m solution. How many grams of caffine were in the sample. m = molality
*February 6, 2008 by Lauren*

**Chemistry Help Please!!!**

A radioactive substance has a half-life of 4 days. Suppose we have 800 mg of this substance. a) Find the equation of the mass remaining after t days. Use the exact value for k not a decimal approximation. b) Rounding your answer to the nearest tenth of a mg, find the mass ...
*April 7, 2014 by Taylor*

Pages: **1** | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | Next>>