# 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.

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)

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

## 2 thoughts on “The railway crossing gate consists”

• questionsolutions Post author

We use kilogram to calculate moments, not grams, so the units used were right. You can write it as 2.0825kN if you like though 🙂