1. **Problem statement:** Water flows through a cylindrical pipe with a radius of 1.5 cm at a speed of 9 cm/s. We need to find the volume of water flowing through the pipe in 1 hour, expressed in litres. 2. **Formula and concepts:** The volume flow rate $Q$ through a pipe is given by the product of the cross-sectional area $A$ and the flow speed $v$: $$Q = A \times v$$ The cross-sectional area $A$ of a circular pipe is: $$A = \pi r^2$$ where $r$ is the radius. 3. **Calculate the cross-sectional area:** $$A = \pi \times (1.5)^2 = \pi \times 2.25 = 7.0686 \text{ cm}^2$$ (approximate to 4 decimal places) 4. **Calculate the volume flow rate per second:** $$Q = 7.0686 \times 9 = 63.6174 \text{ cm}^3/\text{s}$$ 5. **Calculate the total volume in 1 hour:** There are 3600 seconds in 1 hour, so $$V = Q \times 3600 = 63.6174 \times 3600 = 229,022.64 \text{ cm}^3$$ 6. **Convert cubic centimeters to litres:** Since $1000 \text{ cm}^3 = 1$ litre, $$V = \frac{229,022.64}{1000} = 229.02264 \text{ litres}$$ 7. **Final answer:** The amount of water flowing through the pipe in 1 hour is approximately **229.02 litres**.