Question

A substance has a half-life of 60,000 years and an initial mass of 1,000 grams. How many years will pass before only 250 grams of the substance's parent material is left?

30,000

90,000

120,000

240,000

Answer 1

First off, what is a half life? It's the amount of time it takes for an initial amount to decay to half an amount. So if fairy dust has a half life of 10 years and you have 8 pounds of it, you'll only have 4 pounds of it in 10 years. Another 10 years and you'll have only 2. Another 10 pounds you have 1. Get it?

So do something similar here.

Answer 2

no :l

Answer 3

yes :|

Answer 4

What don't you get? You have to think about it, and I can't think for you I'm afraid.

Answer 5

I think its 30 000

Answer 6

Let's go back to the definition of half-life. What is it?

Answer 7

decay the half amount

Answer 8

Are you expected to use a formula?

Answer 9

I doubt it since 250 is exactly two half lives away from 1000.

Answer 10

Nope

Answer 11

To whom are you saying "Nope"?

Answer 12

He's not using complete sentences or even trying. He's on his own now.

Answer 13

To Kainui

Answer 14

Did you do step 1 and define the variables?

Answer 15

No, as I am lost.

Answer 16

What is the beginning amount?

Answer 17

A substance has a half-life of 60,000 years and an initial mass of 1,000 grams.

Answer 18

120 000 ?

Answer 19

Do you know what "initial" means in the sentence above where it says "an initial mass of 1000 g"?

Answer 20

Oh i meant years, so its 1000 g?

Answer 21

Yes. the beginning amount is 1000 g
Now what is the elapsed time?

Answer 22

60000

Answer 23

How many years will pass

Answer 24

That is the question the problem asks. The elapsed time is what you are supposed to find.

Answer 25

What is the half life?

Answer 26

half life of 60 000 would be 30 000, or did you mean half life as 60 000

Answer 27

"A substance has a half-life of 60,000 years." That's what the problem says. So I ask you...what is the half-life?

Answer 28

60 000

Answer 29

What is the ending amount?

Answer 30

Ending amount..?

Answer 31

"only 250 grams of the substance's parent material is left."
If only 250 grams is left, take a wild guess...what is the ending amount?

Answer 32

ending amount would be 0 as far as im concerned :/

Answer 33

Oh wait is it 250 *

Answer 34

Let's say you have $100 and you go Christmas shopping and when you are done, you have only $10 left.

What is you "ending amount" of money?

Answer 35

10

Answer 36

Now let's make sure you understand half life.
Let's say you have $1000 and every 4 days you spend half of your money. That means that the half life of your money is 4 days. It is now Sunday night. How much money will you have left Thursday night?

Answer 37

500

Answer 38

And what about the following Monday night?

Answer 39

250

Answer 40

And the following Friday night?

Answer 41

62.5

Answer 42

What planet are you living on where half of $250 is $62.50?

Answer 43

125 my bad, was thinking about the 4 days

Answer 44

Now. Let's go back to your problem.
You start with 1000 g of this stuff. The half life is 60,000 years.
How much stuff will be left after 60,000 years?

Answer 45

So the start was 120 000 ?

Answer 46

The start of what?

Answer 47

Half life of 60k so 120/2 = 60

Answer 48

So here's your trouble. You don't know what half life means.

Answer 49

Half life is a period of time.

Answer 50

It's the amount of time it takes for half of something to disappear. For example. When I bake a pie, it's half life is about 30 minutes.

Answer 51

That means my family eats half of it in 30 minutes.

Answer 52

k

Answer 53

So in your problem, because this stuff is radioactive and is decaying, it takes 60,000 years for half of it to disappear.

Answer 54

So we start at time 0 with 1000 grams. How many grams will be left after 60,000 years?