MecMovies 4.0 : M2.5: Shear Strain in a Plate

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The figure shows a triangular plate P Q R S before and after deformation. The base of the triangle is Q R S and it is fixed to the ceiling. The length of the segment Q R is 900 millimeters and the length of the segment R S is 300 millimeters. The apex of the triangular plate is P. The height of the plate is 519.615 millimeters. The angle at Q is 30 degrees and the angle at S is 60 degrees. After deformation, the apex P, extends downwards by 1 millimeter.

Begin by computing the plate dimensions before $P$ deflects downward. The distance from point $R$ to corner $P$ is:

$\tan 30^{\circ} = \frac{length PR}{900 mm} ∴ length PR = 519.615 mm$