When you walk forward on a scooter that was previously at rest, how do you calculate the total momentum of you and the scooter? Measure how far you move forward and how far the scooter moves forward, and add the two. Calculate the forces on the scooter in newtons by multiplying mass and acceleration. Measure how far you move forward and how far the scooter moves backward, and average the two. Calculate the forces on the scooter in newtons by adding mass and acceleration. You don't have to calculate it; you already know that it is zero