Question

PHYSICS PLEASE HELP!

If the half life of a given substance is 65 days, how long will it take for a 100-gram sample of the substance to decay until there is only 25 grams of the radioactive material remaining?

if a sample of radioactive isotopes takes 60 minutes to decay from 200 grams to 50 grams, what is the half life of the isotope?

If a 500.0 g sample of technetium-99 decays to 62.5 g of technetium-99 remaining in 639,000 years, what is the half life of technetium-99?

Answer 1

1) 130 days

100>50>25=2 half lives

So 2×65=130 days

2)30 minutes

Since 200>100>50=2 half lives then one half life is 60÷2=30

3)213000 years since 500>250>125>62.5=3 half lives which takes 639,000 yes then one half life would be that divided by 3

Cheers!