# Density = mass/volume

## Homework Statement

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)

## 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.

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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?

LowlyPion
Homework Helper

## Homework Statement

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)

## The Attempt at a Solution

5.97 e24 KG X 2.2 lbs x 1ft3/62.4lbs = 2.1 e23 ft3...

I dont know what to do after this.

Welcome to PF.

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

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

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

- Warren

Welcome to PF.

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

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

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.

Borek
Mentor
5.97 e24 KG X 2.2 lbs

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.

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.

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

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

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Borek
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?

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

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

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

chroot
Staff Emeritus
Gold Member
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

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

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

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

- Warren

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