2.5 Water jet on a truck
A water nozzle shoots water towards the back of a small stationary van. It has a 3 cm²
cross-sectional area, and the water speed at the nozzle outlet is $V_{jet} = 20 \text{ m s}^{-1}$. As the
horizontal water jet hits the back of the van, it is split in two symmetrical vertical
flows (fig. 2.6). The two opposite vertical jets have same mass flow and same velocity
($V_2 = V_3 = 20 \text{ m s}^{-1}$).
2.5.1. What is the net force exerted on the water by the truck?
2.5.2. What is the net force exerted on the truck by the water?
Now, the truck moves longitudinally in the same direction as the water jet, with a speed
$V_{truck} = 15 \text{ m s}^{-1}$.
(This is a crude conceptual setup, which allows us to approach conceptually the case
where water acts on the blades of a turbine.)
2.5.3. What is the new force exerted by the water on the truck?
2.5.4. What is the mechanical power transmitted to the truck?
2.5.5. How would the power be modified if the volume flow was kept constant, but
the diameter of the nozzle was reduced? (briefly justify your answer, e.g. in 30
words or less)
