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!

Radiation Pressure Force on Earth

  1. Apr 25, 2013 #1
    1. The problem statement, all variables and given/known data
    The intensity of sunlight reaching the earth is [tex] 1360 \frac{W}{m^2}[/tex].
    a.) Assuming all sunlight is absorbed, what is the radiation pressure force on the earth? Give your answer in Newtons. [tex]F_r=[/tex]
    b.) Give your answer as a fraction of the suns gravitational force on the earth. [tex] \frac{F_r}{F_g}= [/tex]


    2. Relevant equations
    Intenisty is given by [tex] I= \frac{P}{A}[/tex] where P power and A is the cross sectional area.
    Force is given by [tex]F=\frac{P}{c}=\frac{IA}{c}[/tex] where c is the speed of light in a vacuum.


    3. The attempt at a solution
    I solved the first part correctly, no problem. I got that the radiation pressure force was [tex] 5.78*10^8 N[/tex]
    For the second part, I simply divided this number by the gravitational force of the sun on the earth, which I found to be [tex] F_g=3.53*10^{22} N [/tex]
    When I divided these two numbers, I got [tex]\frac{F_r}{F_g}= 1.64*10^{-14}[/tex] which of course should have no units. However, the problem asks for units, so I put in Newtons anyways, and I was told the my answer must have dimensions of percent (I wasn't aware a unitless quantity had dimensions). So, I slapped in % sign. I was then told to try again; that I was wrong. What am I missing?
     
  2. jcsd
  3. Apr 25, 2013 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    A fraction of 1 would correspond to 100%. A fraction of 1.64*1014 corresponds to...?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Radiation Pressure Force on Earth
  1. Radiation Pressure (Replies: 16)

  2. Radiation pressure (Replies: 2)

  3. Pressure of radiation (Replies: 2)

Loading...