Question

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 195 grams of a radioactive isotope, how much will be left after 3 half-lives?

Answer 1

So it cuts in half every halflife

Answer 2

You have 3 half lifes

Answer 3

( 195 / 2 ) /2 ... etc.

Answer 4

So we divide it by 2 three times?

Answer 5

hint:
the decay law is:
\[\large M\left( t \right) = {M_0}{e^{ - t/\tau }}\]

Answer 6

Not a good hint^

Answer 7

Yes @yesy7

Answer 8

Tbh that formula scares the crap out of me... I've never seen it before.

Answer 9

You dont need it

Answer 10

So I got 24.4 (i rounded)

Answer 11

Yup youre good.

Answer 12

\[\tau \] is the life time
and M_0 is the mass of your sample at t=0

Answer 13

Oh wow that was easier than expected! Thank you both.

Answer 14

They dont specify lifetime

Answer 15

Please I don't think that 24.4 is the right result, sice we have to apply the decay law

Answer 16

oops..since*

Answer 17

Please note that, we have to apply the decay law @swagmaster47

Answer 18

sorry I meant that \[\tau \] is the half-life