SOLUTION: It is known that the mass, m(t), of a radio-active substance decreases as it decays, and that the equation governing this is m'(t)=-.005m(t) where t is in years. What is the half-l

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Question 256914: It is known that the mass, m(t), of a radio-active substance decreases as it decays, and that the equation governing this is m'(t)=-.005m(t) where t is in years. What is the half-life?
any help would be great!!

Answer by Fombitz(32388)   (Show Source): You can put this solution on YOUR website!
Half life means half of the original amount remains.


Integrate,


where C=m0 when t=0, the original amount of material.

At ,
When ,
Substitute,




t_h=138.6 years, approximately

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