Gravitational Problems
Exercise. The radius of the Earth is 6400 km. Find the mass of the Earth. On the surface of the Earth, the gravitational field strength is 9.81 N/kg. Answer. Recall that he gravitational field strength is given by g = GM/R2, where M is the mass of the Earth, and R the radius. So M= gR2/G = 9.81 x 64000002 / ___ = ___ kg.
Exercise. A rocket reaches a height equal to the radius of the Earth.
Find the gravitatianal field strength.
On the surface of the Earth, the gravitational field strength is
9.81 N/kg.
Answer. The gravitatianal field strength, g = GM/r2,
is inversely proportional to the square of the distance r
from the centre of the Earth.
A height equal to the radius means that the distance is
doubled. Since g is inversely proportional to r2,
the new g is 1/4 of 9.81 = ___ N/kg.
Copyright 2010 by Kai Hock. All rights reserved.
Last updated: 25 September 2010.