# physics

posted by .

3) A satellite is orbiting Earth at a distance of 57 kilometers. The satellite has a mass of 96 kilograms. What is the force between the planet and the satellite? (Hint: Don't forget that the distance between them in the equation represents the distance to the center of the earth, you might have to do a bit of Googling to determine the radius of the earth as well as the mass of the earth).

i'm thinking you multiply the satelite's mass by 9.8 (N/kg) then what?

• physics -

At 57 km above the earth, the acceleration due to gravity is no longer 9.8 m/s².
The force between the satellite and the earth is governed by Newton's law of gravitation, GMm/r², which says that the force of gravitational attraction is proportional to the product of the masses, and inversely proportional to the square of the distance between them. For the distance r, it is important that you calculate the distance from the centre of each object, as suggested in the question.
Here's a site that will help you understand the law. Feel free to do some calculations and post your result for verification.
http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation