Unformatted text preview: Applied Math 250 . Assignment #1 Winter 2009 Note: 4066. A/ 13/ due January 20th Assignments are due by noon on the due date, in the drop boxes across from MC Problem Set 1 #11, ii, #2i,iv, part (a) of #2viii, #3, #4i Other strongly recommended problems (not for submission): #lv, #2vi, part (a) of
#2111, vii, #4iii Hint for #1: The constant of integration should not appear in the DE. You’ll need to
eliminate it. Eg, in #liii differentiation gives 3—; = 1 — K6", but we know K = let—f,
so i“ = 1 — y — 11:. Radiocarbon Dating. An important tool in chbozolosigﬂi research is radiocarbon dating. This is a means of
determining the age of certain wood and plant remains, hence of animal or human bones or
artefacts found buried at the same levels. The procedure was developed by the American
chemist Willard Libby (1908—1980) in the early 19505 and resulted in his winning the Nobel
prize for chemistry in 1960. Radiocarbon dating is based on the fact that some wood or plant
remains contain residual amounts of carbon~l4, a radioactive isotope of carbon. This isotope
is accumulated during the lifetime of the plant and begins to decay at its death. Since the
halflife of carbonl4 is long (approximately 5568 years), measureable amounts of carbon14
remain after many thousands of years. Libby showed that even if a tiny fraction of the orig—
inal amount of carbonl4 is still present, then by appropriate laboratory measurements the
proportion of the original amount of carbon~l4 that remains can be accurately determined.
In other words, if Q(t) is the amount of carbon14 at time t and Q0 is the original amount,
then the ratio Q(t)/Qo can be determined, at least if this quantity is not too small. Present
measurement techniques permit the use of this method for time periods up to about 100,000
years, after which the amount of carbonl4 remaining is only about 4 x 10‘6 of the original
amount. To model the phenomenon of radioactive decay, it is assumed that the rate dQ/dt
at which carbonl4 decays is proportional to the amount (more precisely, the number of
nuclei) Q(t) of carbon—14, with proportionality constant k, remaining at time t. 3.) Express this relationship as a DE for Q(t), but set it up in such a way that k > 0 (you
' may need to insert a minus Sign somewhere—think carefully about whether you have
growth or decay). b) Using the DE, sketch typical solutions as you did in # 2. c) Solve the DE for Q(t), and ﬁnd the solution satisfying 62(0) 2 Q0. Note that It is still
an unknown constant. d) Given the halflife of carbon14 (above), ﬁnd k. e) Suppose that certain remains are discovered in which the current residual amount of
carbon14 is 2 percent of the original amount. Determine the age of these remains. ...
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 Summer '09
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