Solving Shear Strain Problem: Find Vertical Displacement

[byu]

Homework Statement

The support consists of three rigid plates, which
are connected together using two symmetrically placed
rubber pads. If a vertical force of 5 N is applied to plate
A, determine the approximate vertical displacement of
this plate due to shear strains in the rubber. Each pad
has cross-sectional dimensions of 30 mm and 20 mm.
Gr = 0.20 MPa.

Homework Equations

The Attempt at a Solution

http://www.academia.edu/6204124/Chapter_03
It is problem #3-33. I need help understanding the last part,
d =40(0.02083) =0.833 mm
Why do they use 40mm, the horizontal length of the padding. Also, where is this equation coming from?

 

[CWatters]

The last line is just trigonometry. Note that 0.02083 Rad is a very small angle so you can make a suitable approximation for Tan rather than use Tan itself.