Calculating radius from volume

[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 I am given is that the volume V is 20 litres. is there any way i can determine the radius from this?

The answer written is r=0.117m

Thanks for any help guys!

 

[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

 

[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

 

[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?

 

[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?

 

[scottie_000]

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

 

[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!

 

[scottie_000]

Glad to help