contestada

Element X decays radioactively with a half life of 9 minutes. If there are 610grams of
Element X, how long, to the nearest tenth of a minute, would it take the element to
decay to 124 grams?
y = a(.5) t/h

Respuesta :

LammettHash

A half-life of 9 minutes corresponds to a decay factor k such that

[tex]\dfrac12=e^{9k}\implies k=-\dfrac19\ln\left(\dfrac12\right)[/tex]

Then the time it takes for the substance to decay from 610 g to 124 g is time t such that

[tex]124\,\mathrm g=(610\,\mathrm g)e^{kt}[/tex]

Solve for t :

[tex]\dfrac{62}{305}=e^{kt}[/tex]

[tex]\ln\left(\dfrac{62}{305}\right)=kt[/tex]

[tex]t=\dfrac1k\ln\left(\dfrac{62}{305}\right)\approx20.686[/tex]

so it takes about 20.7 min for the 610 g sample to decay down to 124 g.

Otras preguntas