If you hit another object with your vehicle, your will be slowed or stopped by the force of impact caused by that object upon impact.

The answer is the vehicle. At the precise moment of the impact in a collision, there is the release of energy when a vehicle strikes another vehicle or another object. Earlier to an impact, a vehicle and everything inside the vehicle is traveling at whatever speed the vehicle had been going. As the collision continues, the vehicle slowly loses energy. However, the vehicle occupants and any others items in the vehicle continue to move forward at the same speed as the vehicle had been traveling prior to impact.