Question

which of the following best explains how a person can jump into the air?
a the person uses her legs to push herself up off of the ground with a force equal to her weight.
b the person pushes down on the floor with a force equal to her weight, causing the floor to exert an upward force on the person equal to her weight.
c the person uses her legs to push herself up off of the ground with a force greater than her weight.
d the person pushes down on the floor with a force greater than her weight, causing the floor to exert an upward force on the person greater than her weight.

Explanation:

To jump, a net upward force is needed. By Newton's third law, when a person pushes down on the floor with a force greater than their weight (action), the floor exerts an equal and opposite upward force (reaction) greater than their weight. This net upward force accelerates them upward. Option D correctly describes this: the person pushes down with > weight, so floor pushes up with > weight. Option A: Force equal to weight would give net force zero (no acceleration upward). Option B: If person pushes with equal weight, floor's reaction is equal, net force zero. Option C: The force on the floor (action) and from floor (reaction) are equal; the key is the force magnitude relative to weight for net upward force.

Answer:

D. The person pushes down on the floor with a force greater than her weight, causing the floor to exert an upward force on the person greater than her weight