If a vehicle is traveling at 55 mph, how fast will unbelted occupants be going at the moment of impact?

Answer: C — 55 mph

When a vehicle traveling at 55 mph experiences a sudden stop due to an impact, unbelted occupants will continue to move at the same speed of the vehicle at the moment of impact, which is 55 mph. This occurs because of inertia, the principle that an object in motion will stay in motion unless acted upon by an external force. In the case of a collision, the vehicle stops, but the occupants who are not restrained by seat belts will continue to move forward at that same speed until they collide with something inside the vehicle, such as the dashboard, windshield, or another occupant. Thus, the correct answer emphasizes the concept of inertia and the physics of motion, highlighting the importance of seat belts in preventing such dangerous outcomes in a crash.