Final answer:
The momentum of the 100 kg running back moving at 3.5 m/s is 350 kg·m/s.
Step-by-step explanation:
The momentum of an object is calculated by multiplying its mass by its velocity. In this case, the running back has a mass of 100 kg and is moving at a speed of 3.5 m/s. To find the momentum, we use the formula momentum = mass x velocity. Plug in the values: momentum = 100 kg x 3.5 m/s = 350 kg·m/s.