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: Radiation Pressure problem

  1. Jan 23, 2016 #1
    1. The problem statement, all variables and given/known data
    t has been proposed that a spaceship might be propelled in the solar system by radiation pressure, using a large sail made of foil.

    Assume that the mass of the ship + sail is 1780.4 kg, that the sail is perfectly reflecting, and that the sail is oriented perpendicular to the Sun's rays. How large must the surface area of the sail be if the radiation force is to be equal in magnitude to the Sun's gravitational attraction?

    The rate at which the Sun emits energy is 3.90 × 1026 W. The Sun's mass is 1.99 × 1030 kg. The gravitational constant is 6.67 × 10-11 N m2/kg2.

    2. Relevant equations
    Preflect= 2Ef cos2ϑ /c

    3. The attempt at a solution

    Ef= (3.9×1026 W)/A = (3.9 ×1026)/ 4πR2 = 3.1×1025/R2

    let surface area be Af :

    force on ship= Preflect Af= (2×3.1×1025×cos20)(Af)/ 3×108×R2

    F= 2.07×1017 (Af)/R2

    Fgravitational at R= GMm/R2 = (6.67×10-11×1.99×1030×1780.4)/R2

    let F=Fgrav =(6.67×10-11×1.99×1030×1780.4)/(2.07×1017)= 1.14 ×106m2 do you agree with my result?
  2. jcsd
  3. Jan 23, 2016 #2


    User Avatar

    Staff: Mentor

    The result looks reasonable. Just over a kilometer square.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted