1. The problem statement, all variables and given/known data A car of mass 1500 kg is at rest on a platform of mass 3000 kg, which is also at rest. The platform has frictionless wheels attached to its bottom. The whole system is initially at rest. The car starts to move forward at a speed of 5.0 m/s with respect to the ground. (Consider all measurements with respect to the ground). What is the momentum of the car as it starts to move? What is the momentum of the car-platform system as the car starts to move? 2. Relevant equations P = mv Ptotal = m1v1 + m2v2 3. The attempt at a solution I was able to solve the first question using the equation P = mv, getting a momentum of 7500 Ns for the car. I don't know how to solve for the momentum of the platform-car system, since the speed of the platform with respect to the ground is not given.