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!

Homework Help: Unit conversion/density

  1. May 27, 2008 #1
    1. The problem statement, all variables and given/known data
    above each square inch of earth's surface is 14.7 lbs of air. the density of air at sea level is about 1.27g/L. the earth is 7930 miles in diameter and has a mass of 5.98 x 10^24kg.
    a.) use the data above to determine the mass in kg of the earth's atmosphere.

    b.) determine the average density of earth in grams per milliliter.

    2. Relevant equations
    i think the only relevant equation is d=m/v. everything else seems to be unit conversions. this problem really isnt about the atmosphere, but rather how well i can convert units, and apparently not well.

    3. The attempt at a solution
    im looking for the mass of the atmosphere, so i use m = dv
    d is 1.27g/mL
    i derive v from 4/3pir^3
    but i have the radius in miles. does this matter?
    i would get (1.27g/mL)(2.55x10^11) since i need it in kg
    (1.27 x 10^-3kg)(2.55x10^11) = 3.24 x 10^8 kg/mL?

    im sure im hopelessly wrong. i dont really want to do part b until i get part a.
    Last edited: May 27, 2008
  2. jcsd
  3. May 27, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    (a) We're given that there are 14.7 pounds of air per square inch of Earth's surface area. If you can figure out how many square inches of surface area the Earth has, can you take it from there?

    (b) The equation you had, d=m/v, applies here.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook