Final answer:
Using Newton's second law of motion, the force applied by the sister to accelerate the skater can be calculated by multiplying the skater's mass (70 kg) by the acceleration (5 m/s^2), which equals to 350 N.
Step-by-step explanation:
The question asks about the amount of force applied by the sister to accelerate a 70 kg skater at 5 m/s2. To solve this, we use Newton's second law of motion which states that force equals mass times acceleration (F = m * a). So, we multiply the mass of the skater (70 kg) by the acceleration (5 m/s2) to calculate the force.
Force = Mass × Acceleration = 70 kg × 5 m/s2 = 350 N
Therefore, the sister applied a force of 350 N to the skater.