# Density = mass/volume

1. Sep 4, 2008

### 964js7

1. The problem statement, all variables and given/known data
The mass of the earth is 5.97 e 24 KG. If density = mass/volume, what would be the density of the earth in pounds/ft(3)

2. Relevant equations

3. The attempt at a solution
5.97 e24 KG X 2.2 lbs x 1ft(3)/62.4lbs = 2.1 e23 ft(3)...

I dont know what to do after this.

Last edited: Sep 4, 2008
2. Sep 4, 2008

### 964js7

The mass of the earth is 5.97 e 24 KG. If density = mass/volume, what would be the density of the earth in pounds/ft(3)

5.97 e24 KG X 2.2 lbs x 1ft(3)/62.4lbs = 2.1 e23 ft(3)...

I dont know what to do after this, or am I even on the right track?

3. Sep 4, 2008

### LowlyPion

Welcome to PF.

$$Density = \frac{POUNDS}{Feet^3}$$

You have converted mass to pounds?
And then what?
What are the other numbers?

4. Sep 4, 2008

### chroot

Staff Emeritus
I have merged these two threads together. Please do not post the same question multiple times.

- Warren

5. Sep 4, 2008

### 964js7

Thank you, but all I got is$${5.97 e ^3}KG$$for a number.... They are asking for the density of the earth in pounds per cubed foot.

6. Sep 4, 2008

### Staff: Mentor

I suppose that was aimed at converting kg to lbs. For that you conversion factor unit should be lbs/kg:

5.97e24 kg * 2.2 lbs/kg = 2.2*5.97e24 kg*lbs/kg

Note, how kg cancels out.

7. Sep 4, 2008

### 964js7

Yes, sorry about not including the conversions in my OP..

http://img293.imageshack.us/img293/4198/92845158ma2.png [Broken]

Last edited by a moderator: May 3, 2017
8. Sep 4, 2008

### Staff: Mentor

Conversion is OK, but then you start making tricks. What is the density definition? If you know the mass, what is the other property of the object that you need to calculate density?

9. Sep 4, 2008

### 964js7

The other property would be volume, but I dont know how to get it with the given info..

10. Sep 4, 2008

### LowlyPion

What volume are you looking to find? Maybe you can find it elsewhere?

11. Sep 4, 2008

### chroot

Staff Emeritus
Yes, you need the radius or diameter of the Earth, as well as its mass, to find its density. If those values are not given, then there is not enough information to answer the question -- unless, of course, you are expected to go look up the radius of the Earth yourself.

- Warren

12. Sep 4, 2008

### 964js7

Should I Just write, not enough info. on my paper? He didnt tell us to search for the radius.

13. Sep 4, 2008

### chroot

Staff Emeritus
If he only gave you one number, and you need two, then yeah -- that's not enough information.

- Warren

14. Sep 4, 2008