If half-life of a substance is $5$ yrs, then the total amount of substance left after $15$ years, when initial amount is $64$ grams is:

16

grams

No worries! We‘ve got your back. Try BYJU‘S free classes today!

2

grams

No worries! We‘ve got your back. Try BYJU‘S free classes today!

32

grams

No worries! We‘ve got your back. Try BYJU‘S free classes today!

8

grams

Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses

Open in App

Solution

The correct option is D $8$ grams
Let us consider the problem.
Half life $= 5 y e a r$
Initial amount of substance $= 64 g r a m s$
$T o t a l t i m e e l a p s e d T = 15 y e a r s$
Therefore
For 5 years, the 64 grams will be reduced to 32 grams
For 10 years this 32 grams will be further reduced to 16 grams
and in 15 years this 16 grams will be reduced to 8 grams
Thus, D is the correct answer.

Suggest Corrections

Similar questions

Q. A radioactive substance decays at an annual rate of

13

percent. If the initial amount of the substance is

325

grams, which of the following functions

f

models the remaining amount of the substance, in grams,

t

years later?

Question 139

A half-life is the amount of time that it takes for a radioactive substance to decay one-half of its original quantity.
Suppose radioactive decay causes 300 grams of a substance to decrease $300 \times 2^{- 3}$ grams after 3 half-lives. Evaluate $300 \times 2^{- 3}$ to determine how many grams of the substance is left.
Explain why the expression $300 \times 2^{- n}$ can be used to find the amount of the substance that remains after n half-lives.