In a radioactive substance, the mass m grams and time t years is given by m=m0e^(-0.03t), where m0 is the original mass

a)If the original mass is 400 grams, what is the mass after 5 years?

b)How long does it take for the substance to decay to half its original mass?

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# log question

Started by jambo david, Apr 25 2006 07:56 PM

4 replies to this topic

### #1

Posted 25 April 2006 - 07:56 PM

### #2

Posted 25 April 2006 - 08:03 PM

a) work out t=1,2,3,4,5

b) 200 = 400 e^(-0.03t)

1/2 = e^(-0.03t)

taking logs of boths side will cancel out the e part leaving you to solve for t

b) 200 = 400 e^(-0.03t)

1/2 = e^(-0.03t)

taking logs of boths side will cancel out the e part leaving you to solve for t

If i am not here i am somewhere else

### #3

Posted 25 April 2006 - 08:17 PM

For part (a), all you have to do is find

*m*when*t*= 5. This is because the formula tells you the mass after*t*years. Also is the original mass, so .### #5

Posted 25 April 2006 - 09:00 PM

that is the value for the new m. For a decimal answer you would use a calculator

cant believe i didnt say what steve said. I just not thinking these days anyhooo

cant believe i didnt say what steve said. I just not thinking these days anyhooo

If i am not here i am somewhere else

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