The railway crossing gate consists 2


The railway crossing gate consists of the 100-kg gate arm having a center of mass at G_a and the 250-kg counterweight having a center of mass at G_W. Determine the magnitude and directional sense of the resultant moment produced by the weights about point A.

The railway crossing gate consists

Image from: Hibbeler, R. C., S. C. Fan, Kai Beng. Yap, and Peter Schiavone. Statics: Mechanics for Engineers. Singapore: Pearson, 2013.

Solution:

Let us write a moment equation around point A. We will assume clockwise movement to be positive.

\circlearrowright M_A=(-100\times 9.81)(2.5+0.25)+(250\times 9.81)(0.5-0.25)

M_A=-2082.5\,\text{N}\cdot\text{m}\circlearrowright
(Notice how we got a negative answer. It simply means the moment being produced is in a counterclockwise direction)

M_A=2082.5\,\text{N}\cdot\text{m}\circlearrowleft\text{(counterclockwise)}

 

This question can be found in Engineering Mechanics: Statics (SI edition), 13th edition, chapter 4, question 4-11.

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