The half-life of platinum-197 is 20 h. How long will it take for a 500-g sample to decay to 125 g?

Question

Multiple Choice of:

a) 10 h

b) 40 h

c) 20 h

d) 80 h

Answer 1

The term "half-life" means that after that amount of time 1/2 of the original amount will have decayed away.

 

In this problem you begin with a sample of 500 g. After 20 hours, 250 grams will remain. 20 hours from this point the sample will be 1/2 of this or 125 g. That is a total of 40 hours. Choice b should be selected here.