Imagine That a New Monorail System Is Being Planned for Sydney

Multiple Choice

Imagine that a new monorail system is being planned for Sydney. The trains will run on elevated tracks, 20 m high. A single square concrete post supports each segment of the track. Each segment of track needs to be able to withstand a sideways force of 100 000N without moving sideways by more than 1 mm. How wide must the concrete support post be? You may assume that the force shears the concrete support posts. The shear modulus of concrete is 2.2x109 N m-2.

A) 100 cm.
B) 95 cm.
C) 90 cm.
D) 75 cm.
E) 32 cm.