# WEBASSIGN DUE at 12:00 in the afternoon today HELP

1. Jun 9, 2009

### xX1SHOt

1. The problem statement, all variables and given/known data

I have a problem that is urgent and due at 12 afternoon today. I will give you the problem and i dont know if you will get it or not in time. It deals with uncertainties in mass and volume to create a specific density with a new uncertainty. Here is the problem:

The radius of a solid sphere is measured to be (6.30 +or- 0.25 ) cm, and its mass is measured to be (1.80 +or- 0.01) kg. Determine the density of the sphere in kilograms per cubic meter and the uncertainty in the density. (Use the correct number of significant figures.)(4 for both answer and uncertainty)

([4sigfigs]_________ +or- [4sigfigs]_______) kg/m^3 note the change from cm to m

i have the first part correct with the exact first answer being 1718 kg/m^3 but entering 1.720 b/c of the multiplication.

2. Relevant equations

already know how to do the first part.

3. The attempt at a solution

have no idea what to do considering the cubing of the converted m from cm and how to deal with the mass as well

sorry if it was brief but i was in a hurry and im sure everyone can do the first part i just need to know the steps to the error bounds

Last edited: Jun 9, 2009
2. Jun 9, 2009

### Hootenanny

Staff Emeritus
Welcome to Physics Forums.

How do you normally account for errors when dividing two quantities?

3. Jun 9, 2009

### xX1SHOt

well normally i would add them together but what do i do with the cubed and how do i account for it

4. Jun 9, 2009

### Hootenanny

Staff Emeritus
Yes but how do you add them? You can't simply take their sum ...

5. Jun 9, 2009

### xX1SHOt

do (4/3)*pi*(.0025)^3 then add the .01

Please just tell me the steps for this time i want to learn it but it is due in 20 minutes.
Please just write out the steps and then i can figure it out hopefully for now

6. Jun 9, 2009

### Hootenanny

Staff Emeritus
I'm afraid that that's not right, in fact it's not even close. Have you been given any notes on error propagation? Now might be a good time to look through them.
That's not the way it works here. We don't do people's work for them.

7. Jun 9, 2009

### xX1SHOt

ive looked at alot of stuff on the internet and no there were no notes in class and it is not described in this application in the book, but thanks for trying to help for now anyway, ill post later after my class to actually understand how this works

8. Jun 9, 2009

### Hootenanny

Staff Emeritus
I think it's a little unfair to set an assignment if you haven't been given any notes on the topic. Here's a decent set of notes: http://hug.phys.huji.ac.il/PHYS_HUG/MAABADA/mitkademet_a/errors.pdf [Broken]. However, only the section on independent variables is relevant for you.

Last edited by a moderator: May 4, 2017