Question

what should a free - body diagram look like for a skydiver who has opened his parachute and is now slowing down as he falls?
there is only an arrow down for gravity.
there is an arrow up for air resistance and an arrow down for gravity. the arrows are the same length.
there is an arrow up for air resistance and an arrow down for gravity. the arrow up is longer than the arrow down.
there is an arrow up for air resistance and an arrow down for gravity. the arrow up is shorter than the arrow down.

Explanation:

When a skydiver opens the parachute and slows down, the net force is upward. According to Newton's second law \(F = ma\), if the skydiver is decelerating (slowing down while falling), the acceleration \(a\) is in the opposite direction of the velocity (upward). The two forces acting on the skydiver are the downward force of gravity (\(F_g=mg\)) and the upward force of air resistance (\(F_{air}\)). Since \(F_{net}=F_{air}-F_g = ma\) (with \(a> 0\) upward), \(F_{air}>F_g\). In a free - body diagram, the length of the arrow represents the magnitude of the force. So the arrow for air resistance (upward) should be longer than the arrow for gravity (downward).

Answer:

There is an arrow up for air resistance and an arrow down for gravity. The arrow up is longer than the arrow down.