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Homework Help! First day NOOB to physics

  1. Jan 20, 2006 #1
    I am new to physics and have bought the dummies books and help guides, I just cant grasp it, and it doesn't help I stink at algebra, can someone PLEASE help me with these 2 questions in detail so I can understand what I am doing wrong. Thank you SO much.

    Convert .998 grams/cm^3 to kg/m^3

    I understand that .998 grams is .000998 kg , and I know that 100cm = 1 meter but I don't know what to do with this information.

    second questions is
    The radius of the earth is 6.37X10^6 meters. Determine the volume of the earth to the correct number of sig figures.

    I am forever grateful to those whole could help a lost soul
    Last edited: Jan 20, 2006
  2. jcsd
  3. Jan 20, 2006 #2


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    First Question hint: would you be able to just convert grams to kiligrams? or just cm to meters? try doing the first step(grams to kgs) then i'll get back to you.

    Second question hint: What is the formula for the volume of a sphere? Remember geometry?

    Show some work and i'll be able to help you a little better.
  4. Jan 20, 2006 #3

    James R

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    Conversion factors:

    1 kg = 1000 grams = 10^3 grams
    1 m = 100 cm


    1 m^3 = (100)^3 cm^3 = 10^6 cm^3

    Or, going the other way:

    1 gram = 10^-3 kg.
    1 cm^3 = 10^-6 m^3


    0.998 g/cm^3 = 0.998 (10^-3 kg)/(10^-6 m^3)
    = 0.998 (10^3) kg/m^3
    = 998 kg/m^3
  5. Jan 20, 2006 #4

    Ok volume of a sphere is 4/3(3.14)r^3

    or in my case 4/3(3.14) 6.37x10^6^3

    Im not sure how to solve this equation though, like in what order.
  6. Jan 20, 2006 #5

    Hey thanks a lot for taking the time it really helped me out and I was able to solve the next two similar ones. Thanks again
  7. Jan 20, 2006 #6


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    Be careful here. Some parenthesis would help to make sure that you do things in the right order. Without them, depending on what kind of calculator or computer you're using, you might be dividing 4 by the rest of the equation.
  8. Jan 20, 2006 #7

    I was too :) I figured out the answer though, it was just a matter of solving the math in the correct order.
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