1. The problem statement, all variables and given/known data A car starts from rest at a stop sign and accelerates to speed 15m/s in a time of 6 seconds. The mass of the car is 300kg and the mass of the rider is 100kg. What is the force on the rider? 2. Relevant equations I figured the acceleration to be 2.5m/s/s. And I know that F = ma. 3. The attempt at a solution I'm not sure if you calculate the force on the car and the driver (400kg), or just the force on the driver (100kg). So the equation is either F=(100)(2.5) or F=(400)(2.5). Which one? Do the car and driver act as one mass?