A brass bearing pad $5.0\ \text{cm}$ thick, with a square face $25\ \text{cm}$ on a side, is bolted down by its lower face. A machine drags its upper face sideways with $1.8 \times 10^{4}\ \text{N}$. How far does the upper face shift? (Shear modulus of brass $3.6 \times 10^{10}\ \text{Pa}$.)