Applications of Bernoulli's theorem can be seen in

A non-viscous fluid with constant density of $1000 \mathrm{kg} {\mathrm{m}}^3$ flows in a streamline motion along a tube of variable cross-section.

The area of cross-section at two $P \text{and} Q$ at lengths $5 \mathrm{m}$ and $3 \mathrm{m}$ are $40 {\mathrm{cm}}^2 \text{and} 20 {\mathrm{cm}}^2$, respectively. If the velocity of fluid at $P$ is $3 \mathrm{m} {\mathrm{s}}^{-1}$, then find velocity of fluid at $Q$.