1. Aug 24, 2007

1. The problem statement, all variables and given/known dataWhat is the area, and its approximate uncertainty, of a circle of radius 3.9 104 cm? (Hint: Assume an uncertainty in the radius of 0.1 104 cm. Use the correct number of significant figures in your answers.)

2. Relevant equationsI really don't know

3. The attempt at a solutionThere's been a lot and scattered on paper...so I don't have one

2. Aug 24, 2007

### rootX

what's the area of a circle?

3. Aug 24, 2007

3.14r^2

and I did that and it wasn't the right answer...

4. Aug 24, 2007

### rootX

is that 14 in "14r^2"

it should be pi.r^2

5. Aug 24, 2007

### Dick

I can't read either one of you. What is a radius "3.9 104 cm" and why should "3.14r^2" be taken to have "14" in it? Is my browser rendering things wrong? Oh, yeah and since when are we using '.' for multiplication as in "pi.r^2"? You may be confusing each other.

Last edited: Aug 24, 2007
6. Aug 24, 2007

### rootX

oops sorry..
I thought 3 is a number (like those question numbers)..

edit: I need to get a sleep :zzz:

7. Aug 24, 2007

### mgb_phys

Error propoagation is to do with how much effect errors have in the calculation.
Simple example speed, if I know the distance to 10% and the time to 10% then the biggest error I could have in speed is 20% ( try some numbers if you aren't sure why)
Whre two numbers are multiplied the percentage errors add.

In area if I know the length to 10% and the width to 10% the worst error I could have is 20%.