Explains why earth's orbital speed varies over the course of each year. explains why earth orbits the sun at a faster average speed than mars. explains why a spaceship with no forces acting on it will continue moving even if it has no fuel. explains why applying a force to a baseball with your arm can cause the baseball to accelerate from rest to the speed at which it leaves your hand. tells us that, when your are standing, the ground is pushing up on you with a force that precisely balances the downward force of your weight. explains why earth's distance from the sun varies over the course of each year.

Check the explanations.

Explanation:

The Earth moves around the sun, but since the universe is in expansion, that is, the distance among the Earth and the Sun is bigger each year, that is the reason why the speed increases.

Mars is a planet that is far away from the Sun than the Earth, so Mars orbit is bigger than Earth´s orbit, so it takes more time to go around the Sun.

A rocket will continue moving around a planet like a satellites around the Earth, due the effect of gravity force that attracts objects to the center of the planet.

The baseball will add the force of the impulse plus the force of the resistance to air against it due to the shape of it. (A rounded object moves with more difficulty than a plat object).

When we move in our Earth, because of the gravity force, our body will be attract to the soil, but at the same time, the resistance of our muscles in the opposite direction will lead a stand up.  

c, this answer is productivity.