A person walking eastward on level ground pushes backward on the ground with her foot…
PHYSICS · Single correct · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A person walking eastward on level ground pushes backward on the ground with her foot during each step. Which explanation below is MOST consistent with why the person accelerates forward instead of remaining at rest?
(a) The person’s leg muscles push her center of mass forward, so no external forces are required for her to accelerate.
(b) Because Earth is so massive, the backward force the person exerts on it is effectively zero, leaving an unbalanced forward force on the person.
(c) The ground exerts a forward static-friction force on the person that is external to the person, so the net force on the person is forward and she accelerates.
(d) The backward and forward forces form an action–reaction pair acting on the person, so they cancel and she continues moving forward by inertia alone.