1. Not finding help here? Sign up for a free 30min 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!

Finding Mass of a Sphere

  1. Mar 21, 2010 #1
    1. The problem statement, all variables and given/known data
    A sphere of metal has a radius of 5.3 cm and a density of 8.15 g/cm3. What is the mass of the sphere? Answer in units of g.


    2. Relevant equations
    Density=mass/volume

    Volume of a sphere=4/3лr^3


    3. The attempt at a solution
    I found the volume by multiplying 4/3 by л and 5.3 squared. I got 66.1850323. I plugged this into the formula for density, manipulated it to get mass by itself and got 539.4118513. This answer seems really unreasonable. I think I need to do some conversions but I'm not sure what to convert. I think I need to convert the radius to meters but the density is in grams/cm cubed and I need to answer in units of grams.
     
    Last edited: Mar 21, 2010
  2. jcsd
  3. Mar 21, 2010 #2
    Mass = density times volume

    First, volume of a sphere is 4/3[itex]\pi[/itex]r^3.

    Next, don't convert anything you've been given the right units for what you've been asked for. Produce a volume for the sphere in terms of cm^3, then

    [itex]cm^3[/itex] * [itex]\frac{g.}{cm^3}[/itex] = [itex]g.[/itex]
     
    Last edited by a moderator: Feb 26, 2015
  4. Mar 21, 2010 #3
    So you're saying find the volume. I got 623.6145193 cm^3. Then I multiply that by the density (8.15) to get the mass. I get 5082.458333. That doesn't seem right. XD
     
  5. Mar 21, 2010 #4
    But it is. Wow. You're amazing! Thanks! XD
     
  6. Mar 21, 2010 #5
    Glad to help.

    Remember that the equation of finding the mass of a sphere is

    Mass = density times volume
     
    Last edited by a moderator: Feb 26, 2015
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook