Earth satellites are objects which revolve around the earth .
Their motion is very similar to the motion of planets around the Sun and hence Kepler’s laws of planetary motion are equally applicable to them .
In particular, their orbits around the earth are circular or elliptic.
A satellite orbiting the earth in elliptical motion will experience a component of force in the same or the opposite direction as its motion. This force is capable of doing work upon the satellite.
Thus, the force is capable of slowing down and speeding up the satellite.
It is low at Equator and high at poles.
Hence, Statement 2 is correct.
The kinetic energy of the satellite in a circular orbit with speed v is
KE =
mv2 =
Hence, Statement 1 is correct.
Considering gravitational potential energy at infinity to be zero, the potential energy at distance (Re+h) from the centre of the earth is
PE =
The K.E is positive whereas the P.E is negative . However, in magnitude, the K.E. is half the P.E, so that the total E is
E = KE + PE =
The total energy of a circularly orbiting satellite is thus negative, with the potential energy being negative but twice is the magnitude of the positive kinetic energy.
When the orbit of a satellite becomes elliptic , both the K.E. and P.E. vary from point to point.
The total energy which remains constant is negative as in the circular orbit case.
This is what we expect since as we have discussed before if the total energy is positive or zero, the object escapes to infinity.
Satellites are always at a finite distance from the earth and hence their energies cannot be positive or zero.
