Question
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.
Pleae get back to us for further clarifications
 
Thankyou
Team
Topperlearning.com
 
Ask the Expert