REAR SEAT PASSENGER OF UBER VEHICLE STRUCK BY ANOTHER VEHICLE IN HIGH IMPACT COLLISION WOUND UP ON FLOOR OF VEHICLE. SHE BELIEVES SHE ENGAGED THE SEAT BELT PRIOR TO COLLISION & QUESTIONS WHY SHE WAS THROWN ON TO FLOOR OF VEHICLE. BOTH VEHICLES IN MOTION. OTHER VEHICLE RAN A STOP SIGN AT 60 MPH ON CITY STREET.