The railway crossing gate consists of the 115- k g gate arm having a center of m
ID: 1861888 • Letter: T
Question
The railway crossing gate consists of the 115-kg gate arm having a center of mass at Ga and the 265-kgcounterweight having a center of mass at GW. Determine the magnitude and directional sense of the resultant moment produced by the weights about point
B
Explanation / Answer
The moment about B is equal to the sum of the Mass*(Gravitational Constant)*(Perpendicular Distance from application to rotation) So....
The moment of Ga with regard to B is 115*9.81*2.5 = 2820.375 N*m. This is positive because it causes a counterclockwise rotation.
The moment of Gw with regard to B is 265*9.81*0.5 = -1299.825 N*m. This is negative becauses it causes a clockwise rotation.
The total moment is simply equal to the sum of the moments, or Moment at B = 2820.375 + (-1299.825) =1520.55 N*m. Since this is positive we know that the final rotation is counterclockwise, and the direction of the moment is in the +Z direction. (Towards the reader)
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