Final answer:
The net external force on Andrea is 291.45 N. To compute her race time, we first use kinematics to find the velocity after the acceleration phase and then calculate the time for both acceleration and constant velocity phases to find the total time.
Step-by-step explanation:
To find the net external force on Andrea, a 67.0-kg sprinter, with an acceleration of 4.35 m/s², we use Newton's second law of motion (F = ma). Multiplying her mass by her acceleration gives us F = 67.0 kg × 4.35 m/s², which equals 291.45 N.To calculate the total time for Andrea to complete a 100.00-m dash, we need to first find the time taken to accelerate for the first 26.00 m. We can use the kinematic equation, v² = u² + 2as, assuming initial velocity u is 0, to find her final velocity v after the acceleration phase. We can then find the time taken to accelerate using the final velocity and acceleration (v = at). For the remaining distance at constant velocity, the time is simply the distance divided by that velocity. Adding both times together will give us the total time for the race.