NonFreeFall Motion and Newton's Second Law of Motion
We are still looking at the man the instant he leaves the stationary plane. Remember: At this point, his velocity is ZERO, and there is ZERO wind resistance acting on him.
The instant he leaves the airplane, the net force acting on the man is just the force due to gravity on the man. We know that the force due to gravity acting on the man is equal to the man's mass multiplied by the acceleration due to gravity, and the force due to gravity always points downward toward the center of the earth.
So, now we know that the sum of the external forces acting on the man the instant he leaves the plane is equal to his mass multiplied by the acceleration due to gravity, and we know this net external force is pointed downward toward the center of the earth.
But, Newton's Second Law of Motion gives us another equation for the sum of the external forces acting on an object.
But, Newton's Second Law of Motion gives us another equation for the sum of the external forces acting on an object.
Let's Combine the Equation for Gravity with Newton's Second Law of MotionFill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button to get a clue. Note that you will lose points if you ask for hints or clues!
Because, at the instant the man leaves the airplane, the only force acting on him is , the net external force acting on the man when he leaves the plane is equal to the of the man multiplied by the due to gravity. According to Newton's Law of Motion, the net external force acting on an object is also equal to the of the object multiplied by the of the object. Because, at the instant the man leaves the airplane, the net external force acting on the man is equal to his mass multiplied by the acceleration due to gravity, and because it is also equal to his mass multiplied by his acceleration, we know that the man's mass times his acceleration must be to his mass times the acceleration due to gravity at the instant he leaves the airplane.

