1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculating radius from volume

  1. Oct 21, 2009 #1
    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"


    Now all im 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!!
  2. jcsd
  3. Oct 21, 2009 #2
    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
  4. Oct 21, 2009 #3
    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
  5. Oct 21, 2009 #4
    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?
  6. Oct 21, 2009 #5
    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?
  7. Oct 21, 2009 #6
    ^(1/3) just means cube root, so is there a button with a 3 in a square root sign?
  8. Oct 21, 2009 #7
    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!!!!
  9. Oct 21, 2009 #8
    Glad to help
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook