1. Oct 21, 2009

### bluffreggie

Hi all,

i am working through some worked examples for my course and there seems to be a step missing.

the step says

"the internal diameter of the vessel can be determined from"

V=PI*r^2*4r

Now all im given is that the volume V is 20 litres. is there any way i can determine the radius from this?

Thanks for any help guys!!

2. Oct 21, 2009

### scottie_000

Assuming the vessel is filled with water, do you know how many litres of water is in a cubic metre? Or how many ml makes up a cubic centimetre?
From there you need to be able to rearrange this equation to solve for r in terms of V

3. Oct 21, 2009

### SinghTutorial

if I say x^3 = 8, is it ok to say x = 2
This problem is just like the one above

V = PI * 4 * r^3

or r^3 = V / ( PI * 4)

so r = ( V / (PI * 4) )^(1/3)

Another this to remember is V is given in liters so you have to convert it into m^3.
20 liters = .02 m^3

and if you plug the above equation in a calculator, you get r = 0.11675m

hope it helps

4. Oct 21, 2009

### scottie_000

Or you could just answer the entire question....
Is it not better to give a few hints, so that the OP will understand how to do it themselves?

5. Oct 21, 2009

### bluffreggie

Ahh i forgot the like terms of the r^2 and r!!!!
i can not seem to get it to work on my calculator.
I get for (V/Pi*4)) = 0.02/Pi*4 = 1.59*10-3
How do i use ^(1/3)?
Is it the abc function?

6. Oct 21, 2009

### scottie_000

^(1/3) just means cube root, so is there a button with a 3 in a square root sign?

7. Oct 21, 2009

### bluffreggie

yeah got it just. thanks mate. That was just the front end of the question. the rest is straight forward just got hung up on the rearrangment side of it. i was close but not close enough!!!!

8. Oct 21, 2009