Section B Answer two questions from this section. Answer in the spaces provided. A hydraulic press is used at a recycling centre to compress waste material. Fig. 7.1 is a side view of the press. [Figure 7.1 (not to scale)] A force to the left is exerted on piston 1. Oil is pushed along the pipe and this moves piston 2 downwards. Piston 2 compresses the waste. (a) Oil is a liquid.

1. (a)(i)State the property of a liquid that makes it suitable for use in a hydraulic system.[1]
2. (a)(ii)Explain, in terms of molecules, why a liquid has this property.[2]
3. (b)Suggest one advantage of using oil as the liquid in a hydraulic press.[1]
4. (c)(i)The cross-sectional area of piston 1 is 0.018m². Piston 1 exerts a force of 4500 N on the oil. Calculate the pressure of the oil due to this force. pressure =[2]
5. (c)(ii)The pressure of the atmosphere is 1.0 × 10⁵ Pa. Calculate the total pressure of the oil in the pipe. total pressure =[1]
6. (c)(iii)The area of piston 2 that is in contact with the oil is 1.4m². Initially, the upper surface of piston 2 is level with point P. Calculate the force exerted on piston 2 due to the pressure calculated in (c)(ii). force =[1]
7. (d)(i)As piston 1 moves along the pipe: • the pressure of the oil in the pipe at point P remains constant • piston 2 moves downwards • the pressure of the oil at the upper surface of piston 2 increases. Explain why the pressure at the upper surface of piston 2 increases.[1]
8. (d)(ii)The density of the oil is 900kg/m³. The upper surface of piston 2 is now 0.50m below the level of the pipe. Calculate the increase in the force exerted at the upper surface of piston 2 by the oil. [gravitational field strength g = 10N/kg] increase in force =[3]
9. (e)There is air trapped in the plastic bags that contain the waste. The temperature of the air in the bags remains constant. Explain, in terms of molecules, why the pressure of the trapped air increases as it is compressed.[3]

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