Gravitation

lydigihome

Q1,
X and Y are two planets. Each of them has a low-altitude satellite revolving in a circular orbit to the planet. If the two satellites are observed to have the same period,

"then X and Y must have nearly the same average density"

why is like that?

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Q2,

An object of mass m is released froma spacecraft at a distance 3R form the centre of the earth which has radius R and mass M. On reaching the earth's surface, the increase in kinetic energy of the object is:
2GmM/3R

how to work it out