Question

Orbital velocity is the average speed of a planet moving through space in its orbit around the sun. Which of the following planets has the fastest orbital velocity? MarsVenusJupiterMercury

Answer 1

The force of gravity is equal to the mass times centripetal acceleration.

Fg = m v^2 / r

The force of gravity is defined by Newton's law of universal gravitation as:

Fg = mMG / r^2

Therefore:

mMG / r^2 = m v^2 / r

MG / r = v^2

v increases as r decreases. So the planet with the smallest orbit (closest to the sun) will have the highest orbital velocity. Of the four options, that's Mercury.