I was driving and going about 50mph and there was no other car near me. Suddenly the car slammed on its brakes. Dropped to probably 10mph. My mom and I were both wearing seatbelts but our heads were thrown forward. My neck and shoulder are sore and stiff today now. There were dark skid marks in the road ahead of us and I believe the car saw those and broke because of them. If there had been a car behind us, we would have be rear ended. There were no warnings beforehand. When the car broke, lights flashed and there was also an alarm. The vehicle has not been inspected by police or manufacturer.