Question

if a runner is accelerating along a flat race track, which statement is true? (1 point)
the gravitational force of the runner on the ground is greater than the normal force of the ground on the runner.
the normal force of the ground on the runner is greater than the gravitational force of the runner on the ground.
the drag on the runner from the air is greater than the running force provided by the runner.
the running force provided by the runner is greater than the drag on the runner from the air.

Explanation:

Step1: Analyze the forces in the vertical direction

According to Newton's third law, the gravitational force of the runner on the ground and the normal force of the ground on the runner are a pair of action - reaction forces. They are equal in magnitude and opposite in direction. So the first two options are wrong.

Step2: Analyze the forces in the horizontal direction

Since the runner is accelerating, according to Newton's second law \(F = ma\) (where \(F\) is the net force, \(m\) is the mass, and \(a\) is the acceleration). In the horizontal direction, the net force \(F_{net}=F_{running}-F_{drag}\). Because \(a> 0\) (accelerating), then \(F_{running}-F_{drag}>0\), which means \(F_{running}>F_{drag}\)

Answer:

The running force provided by the runner is greater than the drag on the runner from the air.