NJC H1 PHY P2 Question

1    NJC 2016  8866/02/16      NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 2 Structured Questions Candidates answer on the Question Paper. No Additional Materials are required. 8866/02 31 Aug 2016 2 hours READ THE 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 soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. The use of an approved scientific calculator is expected where appropriate. Section A Answer all questions. Section B Answer any two questions. Please circle on the front page the questions you are submitting. You are advised to spend about one hour on each section. The number of marks is given in brackets [ ] at the end of each question or part question . For Examiner’s Use Section A (40 Marks) 1 2 3 4 5 Section B (40 Marks) 6 7 8 Total (80m) This document consists of 20 printed pages, including this cover page.

2    NJC 2016  8866/02/16      Formulae uniformly accelerated motion, s= u t + ½ a t2 v2 = u2+ 2as work done on/by a gas, W = pV hydrostatic pressure, p = gh resistors in series, R= R 1 + R2 + … resistors in parallel, 1/R = 1/R 1 + 1/R2 + … Data speed of light in free space, c = 3.00 x 108 m s-1 elementary charge, e = 1.60 x 10-19 C the Planck constant, h = 6.63 x 10-34 J s unified atomic mass constant, u = 1.66 x 10-27 kg rest mass of electron, me = 9.11 x 10-31 kg rest mass of proton, mp = 1.67 x 10-27 kg acceleration of free fall, g = 9.81 m s-2

3    NJC 2016  8866/02/16    Section A Answer all the questions in the spaces provided. 1 (a) (i) By reference to equations of motion, derive an expression for the kinetic energy, Ek, of an object of mass m moving at speed v. [2] (ii) It is often stated that many forms of transport transforms chemical energy into kinetic energy. Explain briefly why a cyclist travelling at constant speed is not making such transformation. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ……………………………………………………………………………….………[2] (b) A car, of mass 720 kg, travelling along a horizontal road with a constant speed of 31 m s-1 would require a power of 36.6 kW. (i) Determine the work done in overcoming the external forces opposing the motion of the car during a time of 5.0 minutes. Work done = ……………………. J [2] (ii) Hence, with reference to (b)(i), suggest, with a reason, whether it would be worthwhile to develop a system whereby when the car slows down, its kinetic energy would be stored for re-use when the car speeds up again. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… …………………………………………………………………………………….…[2]

4    NJC 2016  8866/02/16    2 (a) Show how the conservation of linear momentum can be derived using Newton’s laws. [3] (b) When two strong magnets are held stationary with the north pole of one pushed against the north pole of the other. On letting go, the magnets spring apart. It is apparent that the kinetic energy of the magnets has increased. (i) Explain how the law of conservation of momentum applies in this case. ……………………………………………………………………………………….… ……………………………………………………………………………………….… ………………………………………………………………………………….……[1] (ii) Suggest why the kinetic energy of the magnets increased. …………………………………………………………………………………….…… …………………………………………………………………………………….…… ………………………………………………………………………………….……[1]

5    NJC 2016  8866/02/16    3 (a) Lightning strikes can involve current as high as 25 000 A that lasts for about 40 s. If a person is struck by a bolt of lightning with these properties, the current will pass through his body. The resistance of a human body varies from approximately 500 k (when it is very dry) to about 1.0 k  (when it is wet). The maximum safe current is about 5.0 mA. (i) Define electric current and resistance. Electric Current: ……………… …………………………………………………….... …………………………………………………………………………………………. …………………………………………………………………………………….…[1] Resistance: ……………………………………………………………………...….... …………………………………………………………………………………………. ………………………………………………………………………………….……[1] (ii) How much charges will flow through the person when the lightning described above strikes him? Amount of Charge = ………………..C [1] (iii) What is the largest safe potential difference across a wet human body? Largest potential difference = …………………….V [2]

6    NJC 2016  8866/02/16    3 (b) A car mechanic with an average body resistivity of 5.0  m, is trying to repair a car when his hands accidentally grasp the terminals of a 14 kV car battery with internal resistance of 2000 k. (i) The conducting path between the hands can be represented as a cylinder of 1.6 m long and 0.10 m in diameter. What is the resistance between his left hand and his right hand? Resistance = ………………………  [2] (ii) An electrician claimed that the potential difference between his hands is not equal to 14 kV. Do you agree? Explain clearly. …………………………………………………………………………………………. ………………………………………………………………………….……………[1] (iii) With suitable calculations, determine if the current will kill the car mechanic (i.e. current exceeding the maximum safe current). Current = …………………….A [2] car battery + - left hand grabs here right hand grabs here

7    NJC 2016  8866/02/16    4 (a) State the Principle of Superposition. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ..……………………………………………………………………………………….……[1] (b) In an experiment to determine the speed of sound, a long tube, fitted with a tap, is filled with water. A tuning fork is sounded above the top of the tube as the water is allowed to run out of the tube, as shown in Fig. 4.1 and Fig. 4.2. A loud sound is first heard when the water level is as shown in Fig. 4.1, and then again when the water level is as shown in Fig. 4.2. Fig. 4.1 illustrates a stationary wave produced in the tube. (i) Explain the formation of a stationary wave in the tube. ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………..…………………..… ………………………………………………………………………………………………[2] Fig. 4.1 Fig. 4.2

8    NJC 2016  8866/02/16    4 (b) (ii) Explain why the loudness of the sound changes as the water level changes. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………...… [3] (iii) The frequency of the fork is 512 Hz and the difference in the height of the water level for the two positions where a loud sound is heard is 32.4 cm. Calculate the speed of the sound in the tube. speed of sound = ……………………. m s -1 [3] (iv) The length of the column of air in the tube in Fig. 4.1 is 15.7 cm. Suggest and explain where the antinode of the stationary wave produced in the tube in Fig. 4.1 is likely to be found. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………. .……………………………………………………………………………………………[2]

9    NJC 2016  8866/02/16    5 The loudspeakers L1 and L2 placed 3 m apart emit sound waves of frequency is 680 Hz, in phase. The speed of the sound waves is 340 m s-1.