A GIRLS SECONDARY SCHOOL
the Carth along a path of radius 3.84 x 10"m. The mass of the Moon is
10 and that of Earth is 6.0 x 109. The gravitational force of attraction between the
and the Moon keeps the Moon in orbit, calculate the size of this force (1.99 10 M)
TGM
10kg weighs one-sixth as much on the surface of the moon as on the earth. Calcula
e mass of the moon. The radius of the moon is 1.738 x 10 m. (7.4 X 10 kg)
Trample
A rocket of mass 42000 kg is fired from earth to the moon. What is the net gravitational force on the
rocket when it is 3.00 x 10 m from the centre of the earth? (158 N towards the Earth)
Example
II earth - moon distance 3.8 X 10km, calculate the time in days it takes the moon to circle the eart
Mass of the earth = 5.98 x 10-4 kg.
(27 kg)
Example
Calculate the mass of Jupiter from the knowledge that its satellite lo orbits at an average distance o
4.22 X 10 km from its centre with an orbital period of 42.5 hours. (1.9 x 10-7 kg
2.5 (C) DERIVATION OF KEPLER'S LAW OF PLANETARY MOTION FROM NEWTON'S LAW OF
UNIVERSAL GRAVITATION
Force on the planet
F =mra = m()" - p
w
amway