Final answer:
The mass of the runner is 58.33 kg.
Step-by-step explanation:
To find the mass of the runner, we can use Newton's second law of motion, which states that force equals mass times acceleration. Rearranging this equation, we can solve for mass: mass = force/acceleration.
In the given question, the force on the starting blocks is 700 N and the acceleration of the runner is 12 m/s^2. Therefore, the mass of the runner is 700 N / 12 m/s^2 = 58.33 kg.