Question

how to find
linear speed of mercury planet around the sun

Answer 1

This allows us to determine how much longer and/or shorter the orbital periods of certain planets are, and how much smaller and/or larger their corresponding angular velocities are.

For example,

aEarthaMars≈15.0×1010m≈22.8×1010m

so

TMars≈(22.8×1010m15.0×1010m)3/2(1yr)≈1.87yr

Answer 2

by Newonian mechanics