Arm AB of a classifying accelerometer has a weight of 0.25 lb with mass center at G and...

Arm AB of a classifying accelerometer has a weight of 0.25 lb with mass center at G and is pivoted freely to the frame F at A. The torsional spring at A is set to preload the arm with an applied clockwise moment of 2 lb-in. Determine the downward acceleration a of the frame at which the contact at B will separate and break the electrical circuit.