Fig. 3.1 shows a firefighter directing a jet of water at a wall. [Figure 3.1] In 1.0s, a volume of 7.5 × 10⁻³ m³ of water hits the wall horizontally, at a speed of 24m/s. The density of water is 1000kg/m³.

1. (a)(i)Calculate: the mass of the water that hits the wall in 1.0s[2]
2. (a)(ii)the horizontal momentum of the water that hits the wall in 1.0s.[2]
3. (b)The horizontal momentum of the water decreases to zero when the water hits the wall. None of the water bounces back from the wall. Explain why the momentum calculated in (a)(ii) is equal in size to the horizontal force exerted on the water by the wall.[2]
4. (c)Explain, in terms of Newton's third law, why there is a horizontal force exerted on the wall by the water.[2]
5. (d)The pump that forces the water to flow through the hose is adjusted, and the speed of the water leaving the hose doubles. Explain why the force exerted by the water on the wall increases by a factor of 4.[1]

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