Question

If a parachuter wants to land near his target when should she jump? _________________________________
Explain your answer, which law explains this? WHY?

Answer 1

Answer: She should jump some distance before (upstream of) the target — i.e., before the plane is directly over the target.

Explanation: When she leaves the plane she keeps the plane's horizontal speed. Gravity acts downward, so her horizontal and vertical motions are independent: the horizontal speed stays (approximately) constant while she falls. Because of this forward motion she will land ahead of the point where she jumped unless she leaves earlier so that the forward travel during descent brings her to the target. This is explained by Newton’s first law (law of inertia) and the independence of horizontal and vertical motion in projectile motion: with no horizontal force, the parachuter continues in horizontal motion. (In practice you also account for air resistance and wind when choosing the exact distance.)