Question What kind of force must emergency brakes use? Answers Air pressure Mechanical Heavy Electrical Explanation Because air pressure can eventually leak away, the emergency brakes in an air brake system must be held on by mechanical force. This questions appears in the following tests: West Virginia Knowledge Test Class B , New Jersey Knowledge Test Class B , Utah Air Brakes , Maryland Air Brakes , Pennsylvania Air Brakes , South Dakota Air Brakes , South Carolina Air Brakes ,