Respuesta :
Answer:
The time it'd take for the element to have 15 g of mass is approximately 68 min.
Step-by-step explanation:
The radioactive decay of a substance is given by the following formula:
[tex]mass(t) = mass(0)*e^{-\lambda*t}[/tex]
Since the element has a half life of 12 minutes, this means that after this time the mass of the element will be half of it was originally, therefore:
[tex]\frac{mass(0)}{2} = mass(0)*e^{-\lambda*12}[/tex]
[tex]\frac{1}{2} = e^{-\lambda*12}[/tex]
[tex]ln(\frac{1}{2}) = -12*\lambda\\\lambda = -\frac{ln(0.5)}{12} =0.0577623[/tex]
Therefore the mass of the element is given by:
[tex]mass(t) = mass(0)*e^{-0.0577623*t}[/tex]
If the initial mass is 760 g and the final mass is 15 g, we have:
[tex]mass(t) = mass(0)*e^{-0.0577623*t}\\\\15 = 760*e^{-0.0577623*t}\\\\e^{-0.0577623*t} = \frac{15}{760}\\\\ln(e^{-0.0577623*t}) = ln(\frac{15}{760})\\\\-0.0577623*t = ln(\frac{15}{760})\\\\t = \frac{ln(\frac{15}{760})}{-0.0577623}\\\\t = 67.9555[/tex]
The time it'd take for the element to have 15 g of mass is approximately 68 min.
