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Homework Help: Probably a very novice question

  1. Apr 15, 2012 #1
    Hello everyone! I am new to the forum and it looks an excellent forum, and busy too, which is always good! I feel a bit of a novice for asking this, but i have never been that great at Maths or Physics, so bear with me please.

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

    Basically, i would like to know please, if i was dealing with a density which has a minus at the end of the cubic metres, how do i go about that?

    I need to work out the density of an object with the calculation...

    5 x 103 kg m-3

    2. Relevant equations

    3. The attempt at a solution

    Im guessing that when there is 5 x 103 that means 5 x 30,000?

    But it is just the m-3 which then confuses me.

    Many thanks and again sorry for the novice post.
  2. jcsd
  3. Apr 15, 2012 #2
    the m-3 is just the unit; it means that for every cubic meter the mass is 5000 kg. Density is Mass/Volume.
    The density given is [tex]5000 \frac{kg}{m^3}[/tex]
  4. Apr 15, 2012 #3
    Thanks MrWarlock616, appreciate your quick and helpful reply.

    So (again, sorry if it's a novice question), the - doesnt have any significance?

    Do i not have to minus anything from the calculation or anything like that?

    Thanks again.
  5. Apr 15, 2012 #4
    No, you don't have to subtract anything. Just use 5000 as the density. The minus indicates that cubic meter is in the denominator.
  6. Apr 15, 2012 #5
    Ah right! Thank you again for the explanation and the advice!

    Much appreciated.
  7. Apr 15, 2012 #6
    Sorry, i still seem to be struggling with this, and not sure why, it is frustrating.

    It is thought that the object was around 4.6 m across. Assume the body is a sphere, with a density of

    5 x 103 kg m-3

    i am required to work out the mass of the object.

    This is really annoying me as i cant work it out! Thanks again for any help.
  8. Apr 15, 2012 #7
    Density is ##\frac{Mass}{Volume}##. So the Mass to be found is


    Volume of a sphere is ##\frac{4}{3}\pi r^3##.

    But the object is 4.6 meters across. Hence the diameter of the sphere is 4.6 meters.
    So the radius ##r=2.3##

    Now use the formulae I gave you.

    I love using LaTex
  9. Apr 15, 2012 #8
    Thank you!


    The, if the radius is 2.3, the volume of the sphere =


    The density is 5000kg m3

    Then the mass =

    254825.0521081800 kg
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