Splung.com Physics Forum
Discuss physics or ask questions. Part of the Splung.com physics web site.

Author Message
dumperdery

Joined: 23 May 2010
Posts: 4

 Posted: Tue Jun 01, 2010 5:56 pm    Post subject: Physics Problem 3 - Gravitation, Newton's Law of Gravity A spaceship is launched and starts moving directly towards the Moon. At what distance from the Earth will the pull of the Moon on the spaceship exceed the pull of the Earth? Ignore the effect of the Sun in this calculation.
hepcj

Joined: 23 Jun 2007
Posts: 125

 Posted: Tue Jun 01, 2010 8:57 pm    Post subject: This a one dimensional problem in which you must calculate the force due to the Earth and the force due to the moon. Using Newton's law of gravity, we have: F(r)_Earth = (G M_Earth m)/ (r)^2 and for the moon: F(r)_Moon = G M_moon m/(d-r)^2 We are using the distance d to be distance from the centre of the Earth to the centre of the moon. Obviously, as the ship moves away from the Earth, it moves closer to the moon and at any time so the equations are linked. Since we want the forces to be equal we can equate them, G M_moon m/(d-x)^2 = G M_Earth m/x^2 cancelling G and m, we are left with: M_moon / (d-x)^2 = M_Earth/ x^2. Solve for x and take away the radius of the Earth as the question asks for the distance from the Earth.
 Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First
 All times are GMT Page 1 of 1

 Jump to: Select a forum Physics Forum----------------Physics Help. Ask a Physics ExpertPast Papers
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum