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Situation:A 34 gram sample of a substance that's used to treat thyroid disorders has a k-value of 0.137.N= Noe-ktNo initial mass (at time t = 0)N = mass at time tk== a positive constant that depends on the substance itself and on the units used to measure timet = time, in daysFind the substance's half-life, in days.Round your answer to the nearest tenth.

User Chappar
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1 Answer

16 votes
16 votes

Answer:

5.1 days

Explanation:

The half-life of a substance is the time it takes the substance to decay to half of its initial mass.

The function that models the decay of the substance is:


N=N_oe^(-kt)

• The initial mass, No = 34 grams

,

• Half of the initial mass, N = 34/2 = 17 grams

,

• k=0.137

Substitute these values into the formula:


17=34e^(-0.137t)

The equation is then solved for t:


\begin{gathered} \text{ Divide both sides by 34} \\ (17)/(34)=(34e^(-0.137t))/(34) \\ e^(-0.137t)=0.5 \\ \text{ Take the }\ln\text{ of both sides} \\ \ln(e^(-0.137t))=\ln(0.5) \\ -0.137t=\ln(0.5) \\ \text{ Divide both sides by -0.137} \\ (-0.137t)/(-0.137)=\frac{\operatorname{\ln}(0.5)}{-0.137} \\ t=5.06 \\ t\approx5.1\text{ days} \end{gathered}

The substance's half-life is 5.1 days (rounded to the nearest tenth).

User PEM
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