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: Gravitational Field Strength

  1. Nov 17, 2014 #1
    1. The problem statement, all variables and given/known data
    70d030c2091bcb8514dcab3cf06abd76.png
    2. Relevant equations
    g = GM / r^2, where g is the gravitational field strength, G is the gravitational constant, M is the mass of the attracting body, r is the radius of the attracting body.
    p = M / v, where p is density and v is the volume.
    Vs = 4/3 * pi * r^3, where Vs is the volume of a sphere, r is the radius of the sphere.
    3. The attempt at a solution
    g = M / r^2 (as G is constant)
    rearraging p = M / v, M = pv
    pv / r^2 = g
    (p * 4/3 * pi * r^3) / r^2 = g (assuming the planet is perfectly spherical)
    p * 4/3 * pi * r = g
    density of Q is 1/2 that of P, radius is 2x that of P.
    1/2 * 4/3 * pi * 2 = 4/3 * pi
    therefore, 4/3 * pi * 13.4 = 56.13Nkg^-1, however the answer is 13.4Nkg^-1? Can someone see where I've gone wrong?
     
  2. jcsd
  3. Nov 17, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    4/3 is a constant, and so is pi... just like G.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted