Final answer:
The net external force on a 63.0-kg sprinter accelerating at 4.200 m/s² is calculated using Newton's second law of motion, yielding a force of 264.6 N.
Step-by-step explanation:
The question involves calculating the net external force acting on a sprinter using Newton's second law of motion, which is expressed as F = ma, where F is the force, m represents mass, and a denotes acceleration. Given that the mass (m) of the sprinter is 63.0 kg and the acceleration (a) is 4.200 m/s², the net external force can be calculated as follows:
F = ma = 63.0 kg × 4.200 m/s² = 264.6 N.
Therefore, the correct answer to the question is b) 264.6 N, which is the net external force acting on the sprinter as she starts the race.