Why is ganymede called a moon and not a planet

The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. Galileo's discovery eventually led to the understanding that planets orbit the sun, instead of our solar system revolving around Earth. Galileo called this moon Jupiter III.

the speed increase from w to x due to increased gravity force

the speed decreases from x to y due to decrease in gravity

answer; ///i believe the correct answer is (aids) acquired immune deficiency syndrome;