Question

Two earth-satellites are revolving in the same circular orbit around the center of Earth. They must have the same ___ .

• A. time period
• B. energy
• C. mass
• D. velocity

Answer 1

Answer: (A), (D)

velocity

If two earth-satellites are revolving in the same circular orbit round the center of the earth, then the orbital radius is the same.
According to Kepler's Laws of planetary motion,
$T^2\propto R^3$
where
T: Time period of the satellite
R: Radius of the orbit
As R is the same for both the satellites, time period is equal.

Orbital velocity of the satellite is given by:
$v=\frac{2\pi R}{T}$
As R and T is same for both the satellites, the speeds are equal for the two satellites.
Mass of the two satellites need not be the same. Also, energy of the satellite is dependent on the mass and hence, the energies also need not be the same.