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: Question :S

  1. May 21, 2008 #1

    a.a

    User Avatar

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

    By how much does the mass of the earth increase each year as a result of sunlight reaching it? Radiation from the sun reaches the EArth at a rate of 1400W/m^2 of area perpendicular to the energy flow. Assume 100% absorption.

    2. Relevant equations
    I'm sorry but I havent the slightest clue as to how to approach this question.
    But we are given the Radius of the Earth as 6.36 * 10 ^6 m


    3. The attempt at a solution

    The answer is sopposed to be 1.23 * 10^8
     
  2. jcsd
  3. May 21, 2008 #2

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    I'll give you a hint: What is the area that is seen by the rays coming from the sun?
     
  4. May 21, 2008 #3

    a.a

    User Avatar

    First to answer your question: only half the surface area? Which would be 2pi r^2

    So we have to solve for power useing power = rate * surface area

    then solve for energy useing energy = power * time

    then E = mc^2 to solve for mass..

    Would this mass be the increase or the mass after one year?
     
  5. May 21, 2008 #4

    Dick

    User Avatar
    Science Advisor
    Homework Helper

    Cross sectional area. Not 1/2 of surface area. Cross section, i.e. pi*r^2. And yes, you seem to know how to calculate the rate of energy absorption and solve for the equivalent mass.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook