what happen to the value g (free fall). If the rocket has launch from Earth to moon with the constant velocity. What if the rocket acclerating?
Earth to Moon? On the Moons surface, the acceleration due to gravity (Earth and Moon) points toward the Moon. Otherwise, things would fall off the moon. Now, if anyone would be so unwise as to travel to Earth at constant velocity, they would use a lot of fuel, first to escape the moon, and secondly, as Earth gravity took over, they would have to fire retrorockets to counter the accelerating force due to gravity of Earth.
Be wary of thinking the acceleration due to gravity is constant: it is not, as one goes farther from Earth, "g", decreases.