Thirty kilograms of an unknown substance are observed for two weeks. At the end of the two weeks, only 19 kg of the substance has remained the same (the rest has undergone radioactive decay.) What is the half life of this substance?

a.) 4.0 weeks
b.) 2.0 weeks
c.) 3.0 weeks
d.) 5.0 weeks
e.) 1.0 weeks

Question

Thirty kilograms of an unknown substance are observed for two weeks. At the end of the two weeks, only 19 kg of the substance has remained the same (the rest has undergone radioactive decay.) What is the half life of this substance?
 	
a.) 4.0 weeks
b.) 2.0 weeks
c.) 3.0 weeks
d.) 5.0 weeks
e.) 1.0 weeks

anonymous · Answer

c.) 3.0 weeks Half life in days = (elapsed days * log 2) / log [ beginning mass / ending mass] Half life = 21.2 days or 3 weeks http://www.1728.org/halflife.htm