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Homework Help: Question :S

  1. May 21, 2008 #1


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    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


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    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


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    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


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    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.
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