NJC 2022 Prelim P3

[Turn over NATIONAL JUNIOR COLLEGE SENIOR HIGH 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 3 Structured Questions Candidate answers on the Question Paper. 9749/03 26 Aug 2022 2 hours No Additional Materials are required. READ THE INSTRUCTION FIRST Write your subject class, registration number and name in the spaces at the top of this page. 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 The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 10 2 / 12 3 / 14 4 / 10 5 / 6 6 / 8 Section B 7 / 20 8 / 20 Total (80) This document contains 24 printed pages and 4 blank pages.

2

[Turn over 3

4 Section A Answer all the questions in the spaces provided. 1 If an object is projected vertically upwards from the surface of a planet at a fast enough speed, it can escape the planet’s gravitational field. This means that the object can arrive at infinity where it has zero kinetic energy. The speed that is just enough for this to happen is known as the escape speed. (a) r is the distance from the centre of the planet. On Fig 1.1, draw the variation with distance r of the kinetic energy EK, gravitational potential energy EP and the total energy ET of this object from the surface of the planet. Fig. 1.1 [3] (b) (i) By equating the kinetic energy of the object at the planet’s surface to its total gain of potential energy in going to infinity, show that the escape speed v is given by v2= 2GM R where R is the radius of the planet and M is its mass. [1] energy r surface of planet 0

[Turn over 5 (ii) Hence show that v2 = 2Rg where g is the acceleration of free fall at the planet’s surface. [2] (c) The mean kinetic energy Ek of an atom of an ideal gas is given by Ek = 3 2 kT where k is the Boltzmann constant and T is the thermodynamic temperature. (i) Using the equation in (b)(ii), estimate the temperature at the Earth’s surface such that helium atoms of mass 6.6 × 10–27 kg could escape to infinity. You may assume that helium gas behaves as an ideal gas and that the radius of Earth is 6.4 × 106 m. temperature = ..................................................................... K [3] (ii) The temperature estimated in (i) is measured in thermodynamic scale. Explain what is absolute