Question

which statement explains how planets move in orbit as supported by newtons first law of motion?
planets can change the direction of their own orbital path.
planets can change orbit due to their inertia.
planets in motion will have a constant speed unless acted on by an outside force.
planets with a greater mass will orbit more quickly than smaller planets.

Explanation:

Newton's first law of motion states that an object in motion will stay in motion with a constant velocity (constant speed and direction) unless acted upon by an external force. Planets in motion will have a constant speed unless acted on by an outside force (such as gravitational forces from other celestial bodies) which is in line with Newton's first law. Planets cannot change the direction of their own orbital path without an external force (so the first option is wrong). Inertia is the tendency of an object to resist changes in its state of motion, but planets don't change orbits due to their inertia (the second option is wrong). The speed of a planet's orbit is related to gravitational forces and orbital radius, not just mass (the fourth option is wrong).

Answer:

Planets in motion will have a constant speed unless acted on by an outside force.