Question

state Kepler law of planetary motion 3 mark

Answer 1

thank you for asking this question. There are 3 laws of Kepler for planetary motion. The first law states that "that all planets move in ellieptical orbits around the sun, while sun being the one or two foci. the second law says that "the sun sweeps out equal areas during equal internals of time. The third state kepler's law of planetary motion is a little tricky which says "the squares of the sidereal (orbital) periods of the planets are directly proportional to the cubes of their average distances from the sun". 
hope this answers the question to its full extent clearly. 

Answer 2

Each planet moves around the sun in an elliptical orbit with sun at one of foci.
Kepler second law is the consequences of the law consequences of the law of conversation of angular momentum.
Planets with n nearly circular orbits like mercury, venus and earth, the semi-major and semi minor axis councide with radius R, then
i.e., T2 alpha R3 or T2/ R3= constant
This law is called harmonic law or law of periods