2022 SJI Phy Prelims P2 SectB

15 CANDIDATE NAME CLASS INDEX NUMBER Section B Q9 Q10 Q11E Q11O Section B (30 marks) Answer all questions in this section. Answer only one of two alternative questions in Question 11. 9 A lorry crane as shown in Fig. 9.1 is used in a construction site to lift concrete beams. The boom is pivoted onto the lorry such that the distance from the pivot point of the boom to the lorry’s back wheel is 2.0 m. Fig. 9.1 http://www.acecrane.in/sb-163-lorry-loader-crane-4561877.html Table 9.1 summarises the maximum load that the lorry crane can carry and the corresponding distances from the load to the lorry ’s back wheel when the boom is horizontal. Table 9.1 length of boom / m distance from the load to the lorry’s back wheel / m maximum load / kg 4.0 2.0 3000 6.0 4.0 1500 8.0 6.0 1000 10.0 8.0 750 12.0 10.0 600 2.0 m pivot point of the boom extendable boom

16 (a) Using the data from Table 9.1, state and explain the relationship between the distance from the load to the lorry’s back wheel and the maximum load that the lorry crane can carry. .………………………………………………………………………………………….. …………………………………………………………………………………….…..[2] (b) The weight of the uniform boom is 10 000 N. (i) Calculate the minimum weight of the lorry. Assuming that the distance from the centre of gravity of the lorry to the lorry’s back wheel is 2.5 m. weight = ........................................ [2] (ii) The actual weight of the boom is much heavier than 10 000 N. Explain why when the length of the boom is 4.0 m, the maximum load that can be lifted is the same as the maximum load shown in Table 9.1. .…………………………..……………………………………………………….. ………………...………..………………………………………………….…..[1] (c) Lorry cranes have additional support extended sideways as shown in Fig. 9.2. Fig. 9.2 https://www.cranes.org.nz/uploads/2/0/5/7/20572552/crane_stability_and_ground_pressure.pdf Explain how the additional support increases the stability of the lorry crane. .………………………………………………………………………………………….. …………………………………………………………………………………….…..[1] additional support

17 (d) The concrete beam is freely suspended as shown in Fig. 9.3. Fig. 9.3 (i) Mark the centre of gravity of the concrete beam with the letter ‘x’. Explain your answer. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………….…..[2] (ii) The concrete beam is made of 10% steel and 90% concrete by volume. If the density of steel and concrete is 7800 kg/m 3 and 2400 kg/m 3 respectively, determine the average density of the beam. average density = ........................................ [2] concrete beam

18 10 Fig. 10.1 shows a solenoid that is co