VJC H1 PHY P2

1 Name : ________________________________ CT group : 15S________________ VICTORIA JUNIOR COLLEGE 2016 JC2 PRELIMINARY EXAMINATIONS PHYSICS Higher 1 Paper 2 Structured Questions Candidates answer on the Question Paper No Additional Materials are required. 8866/02 19 Sep 2016 MONDAY 2 pm – 4 pm 2 Hours READ THESE INSTRUCTIONS FIRST Write your name and CT group at the top of this page. 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. Section A Answer all questions. Section B Answer any two questions. 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 2 3 4 5 Section B 6 7 8 Total (max. 80): This question set consists of a total of 19 printed pages.

2 Data speed of light in free space, c = 3.00  108 m s-1 elementary charge, e = 1.60  10-19 C the Planck constant, h = 6.63  10-34 J s unified atomic mass constant, u = 1.66  10-27 kg rest mass of electron, me = 9.11  10-31 kg rest mass of proton, mp = 1.67  10-27 kg acceleration of free fall, g = 9.81 m s-2 Formulae uniformly accelerated motion, s = ut +( ½) at2 v2 = u2 + 2as work done on/by a gas, W = pV hydrostatic pressure, p = hg resistors in series, R = R1 + R2 + … resistors in parallel, 1/R = 1/R1 + 1/R2+ …

3 Section A Answer all questions in this section 1. A traffic policeman hiding behind a signboard detects a car speeding past him with a constant speed of 150 km h-1. He starts his motorcycle 3.0 seconds later and gives chase, accelerating uniformly at 12 m s-2. He overtakes the car at time t1. The time when the car speeds past the policeman is taken to be t = 0.0 s. (a) On the same axes, sketch a speed – time graph for the car and motorcycle. Indicate on the time axis, the moment when the motorcycle overtakes the car as t1. [3] (b) Hence or otherwise, calculate t1. [3] 2. The simplified diagram in Fig 2 represents the trunk of a person bent forward, with the spine at an angle of 70.0o to the vertical. The extensor muscle, which joins the spine to the pelvis, makes an angle of 8.0o to the spinal column. The weight W of the person’s trunk and head, which is 400 N, is shown to act at the point along the spine where the extensor muscle is attached. Pelvis Hip joint pivot W = 400 N Tension T of extensor muscle Head Spine Fig 2 70.0o 8.0o

4 (a) Draw and label an arrow R on Fig 2 to show the direction of the reaction force acting on the spinal column at the hip joint pivot. [1] (b) Explain why there would be no net moments acting on the body. [1] (c) (i) Explain why the tension T of the extension muscle, the weight W and the reaction force R must form a closed triangle. [1] (ii) Hence, or otherwise, calculate reaction force R at the hip joint and the tension T in the extensor muscle. [4]

5 3(a) Define magnetic flux density [1] (b) A rectangular coil of N number of turns is lying with its plane at an angle to a horizontal uniform magnetic field B as shown in Fig 3.1. LM=KN=y and KL=MN=x. The coil carries a current of I. Fig 3.2 shows the view from the side KL. Fig 3.1 Fig 3.2 (i) Draw all the magnetic forces acting on the coil in Fig 3.1. [2] (ii) Derive an expression for the torque  acting on the coil in terms of x, y, N, I, B and . [2] (c) A moving coil galvanometer, as shown in Fig 3.3 is constructed such that the plane of the coil (N turns, area A) remains parallel to the magnetic field B during rotation by using a radial field. Fig 3.4 shows the schematic diagram of the galvanometer. A soft-iron core is fixed centrally between the semi-polar pole pieces of a permanent magnet. The coil is also held centrally between the pole pieces and it has a pointer attached. The coil moves in the space between the soft iron core and the magnet. A restraining torque provided by

6 the spiral springs placed above and below the coil is used to measure the current I flowing through the coil. Fig 3.3 Fig 3.4 Torque provided by current in coil in radial field NBIAcoil  , where A = xy, Restraining torque supplied by spiral springs  kspring  , where k is the spring constant and  is the angle of deflection of the pointer from the zero point. (i) Explain why when the pointer comes to rest, the deflection of the pointer  is proportional to the current in the coil. [2] (ii) Using the results of (b)(ii) and (c)(i), or otherwise, suggest why a radial field is used instead of a uniform field, in a galvanometer. [2]

7 4. Railway signals rely on a combination of resistors to trigger the correct colour of light. Figure 4.1 shows a simplified version of the circuit used. The relay can be considered to be equivalent to a resistor. When the potential difference across the relay is above 3.0 V it switches on the green signal. The signal is red when the relay potential difference is 3.0 V or less. Fig. 4.1 (a) (i) The variable resistor is set to 10 Ω. Τhe relay resistance is 5.0 Ω. Calculate the potential difference across the relay. Assume the railway track has negligible resistance. [2] (ii) When the variable resistance is 10 , the signal is green. Calculate the minimum increase in the variable resistance which will cause the signal to turn red. [2] Figure 1 12 V Railway track Relay

8 (b) The track is laid in sections of 100 m, with a length l between the rails. Each section of track is insulated from the next section. Ballast, usually made of broken up rock, is used to support the track as shown in Figure 4.2. Fig. 4.2 (i) The ballast has a depth of 5.0 cm and a resistivity of 3.4  102 Ω m. Calculate the resistance of this 100 m section of ballast between the rails. [2] (ii) The ballast resistance is in parallel with the relay. Calculate the combined resistance due to the above section of ballast and the 5.0 Ω relay. [2] Figure 2 Ballast average depth 5 cm l = 1.44 m between rails

9 5 . Fig. 5.1 Water from the reservoir falls through a pipe of height h1 and then gives up all of its kinetic energy to a turbine which is connected to an electrical generator. The water is finally discharged into a river. Data for the power station are listed below. height of pipe h1 400 m reservoir depth h2 30 m average area of reservoir 300 km2 density of water 1000 kg m-3 efficiency of power station 40 % power supplied to consumer 500 MW (a) Assuming that the depth of water in the reservoir is negligible compared to the height of the pipe, use the data above to calculate, for a fully filled reservoir, (i) the mass of water available, mass =…………………kg [2] reservoir h2 pipe h1 river