Sun February 27, 2011 By: Vishakha Nair

Hi!Could you pls answr my questions? 1)Half life of a radioactive substance is 10 hours.what %of it will decay in 5 hours? 2)Half life of a radioactive substance is 100 days.If originaly 100mg of the substance was present, what will be left after 5 days?

Expert Reply
Thu March 10, 2011
Dear student,
1. Assume initial quanityt= x, then after 10 years, it becomes x/2
After 5 years, x/4or 25%
2. at t=0, amount = 100gm
at t = 100, amount =50
t=5 amount = 5X50/100 = 2.5gm
amount= 100-2.5 = 97.5gm left
Hope this helps.
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