Question

A certain radioactive element has a half-life of one hour. If you start with 40.0 grams of the element at noon, how much of the radioactive element will be left at 2 p.m.? (3 points)
0.0 grams
10.0 grams
20.0 grams
5.0 grams

Answer 1

need to use the formula---> final amount= initial amount x (1/2)^(t/h), where t is time and h is half-life. time between noon and 2 pm is two hours. half life is 1 hour

final amount = 40.0 g x (1/2)^( 2 hours/1 hour)= 10 grams

Answer 2

Answer:

The correct answer is option D

Explanation:

Half life of the radioactive element is one hour, which means after every one hour its mass reduces by half its previous value

$12: 00 pm\\weight = \frac{40}{2} grams\\= 20 grams\\1:00 pm\\weight = \frac{20}{2} grams\\= 10 grams\\2:00 pm\\weight = \frac{10}{2} grams\\= 5 grams$