NJC H2 Physics Prelim P3 Ans

[Turn over NATIONAL JUNIOR COLLEGE SENIOR HIGH 2 PRELIMINARY EXAM Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 3 Longer Structured Questions Candidate answers on the Question Paper. No Additional Materials are required. 9749/03 25 Aug 2023 2 hours READ THESE INSTRUCTION FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answers all questions. Section B Answer one question only. You are advised to spend one and a half hours on Section A and half an hour on Section B. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 7 2 / 10 3 / 9 4 / 10 5 / 8 6 / 6 7 / 10 Section B 8 / 20 9 / 20 Total (80m) This document contains 28 printed pages and 0 blank pages.

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4 Section A 1 A bungee jumper of mass 60 kg is attached to an elastic rope which starts to stretch after a short time of free fall. The gravitational potential energy of the bungee jumper is 0 J when she has fallen through 40 m to the lowest point. (a) gravitational potential energy / kJ elastic potential energy / kJ kinetic energy / kJ top 0 0 half-way 2.6 bottom 0 Fig. 1.1 Fill up the missing energies at the top, bottom and half-way positions in Fig 1.1. Drag forces can be considered negligible. [2] gravitational potential energy / kJ elastic potential energy / kJ kinetic energy / kJ top 24 (23.5) 0 0 half-way 12 (11.8) 2.6 9.2 (9.17) (accept 9.4) bottom 0 24 (23.5) 0 Fig. 1.1 Fill up the missing energies at the top, bottom and half-way positions in Fig 1.1. Drag forces can be considered negligible. [2] GPE (using mgh) [B1], EPE and KE at half -way and bottom positions (using conservation of energy) [B1] Comments: Most students are able to answer this part. Some students seemed to forget that the total energy is the same regardless of the position. (b) Show that the unstretched length of the elastic rope is 10 m. [2]

5 [Turn over Let the spring constant of the elastic rope be k and unstretched length be x At half-way position, 2.6 = 1 2 𝑘(20 − 𝑥)2 At bottom position, 23.5 = 1 2 𝑘(40 − 𝑥)2 [B1 for equations] 2.6 23.5