RVHS H1 PHY P2 Solutions

River Valley High School Pg 1 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 H1 Prelim 2 (2016) Paper 2 Solutions 1 To estimate the frictional force acting on a truck, the driver puts his truck at the neutral gear (not stepping on the accelerator nor applying any brakes) while moving on a level road. He finds that the speed slows down from 24 km h 1 to 18 km h1 over a distance of 10.5 m. The truck is of mass 1500 kg. (a) (i) Show that the frictional force acting on the truck travelling on the level road is 1400 N. v2 = u2 + 2 as (18000/3600)2 = (24000/3600)2 + 2a(10.5) a =  0.926 f = ma = (1500)(0.926) = 1388 = 1400 N (shown) [1] (ii) Hence or otherwise, determine the power developed by the truck’s engine when it is travelling at a constant speed of 12 m s 1 on the level road . The frictional force can be assumed to be constant. P = fv Constant speed, driving force (from engine) = friction = (1400)(12) = 16800 power = …………………………. W [2] (b) The truck then moves up a gentle slope of 1.0  as shown in Fig. 1 .1. The frictional force acting on the truck along the slope is 800 N. Fig. 1.1 Applying the same power from the engine as (a)(ii), determine the maximum speed that the truck can attain up the slope. Pengine = Pfriction + WD against gravity / t 16800 = 800 v + mg h /t = 800 v + mg d sin 1 /t = 800 v + mg v sin 1 v = … = 15.9 = 16 speed = …………………………. m s1 [3] 1.0  Not to scale

River Valley High School Pg 2 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 2 An air-rifle pellet of mass 2.0 g travels horizontally towards a stationary clay block of mass 56 g. The pellet reaches the block with a speed of 140 m s –1 and remains in the block after the collision. Fig. 2.1 (a) State the principle of conservation of momentum. Total momentum of a system of objects remains constant provided no resultant external force acts on the system. ..………………………………………………………………………………………….. [1] (b) Assuming that the total momentum of the pellet and the block is conserved during the collision, calculate the initial speed of the block after impact. m1u1 = (m1+m2)v (2)(140) = (2+56) v v = 4.8 m s–1 speed = …………………… m s–1 [2] (c) The variation of the momentum of the pellet p with time t is shown in Fig. 2.2. below. The duration of impact (collision) is indicated in the figure. Sketch the variation of the momentum of the block only with time before, during and after the collision. Values of the momentum are not needed in the sketch. [2] Fig.2.2 block pellet block and pellet move together after collision 0 p t Duration of impact

River Valley High School Pg 3 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 [Turn over 3 (a) Define potential difference. energy per unit charge transferred from electrical energy to other form when the charge passes through an electrical component. [1] (b) For the purpose of measuring the electrical resistance of shoes through the body of the wearer to a metal ground plate, the National Standards Institute (NSI) uses the circuit shown in Fig. 3.1. The potential difference Δ V across the 1.00 MΩ resistor is measured with an ideal voltmeter. Fig. 3.1 (i) Show that the resistance of the shoes is given by        V VRshoes 501000.1 6 . ERR RV shoesM M          00.1 00.1 50 1000.1 1000.1 6 6         shoesR V      V VxRshoes 501000.1...... 6 [1] 1.00 MΩ 50.0 V

River Valley High School Pg 4 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 (ii) In a medical test, a current through the human body should not exceed 150 μA. Show with calculations, whether the current delivered by the circuit exceed s 150 μA. State any assumptions made in your calculations. Current through circuit = AA 50105100.1 50 100.1 50 5 66   shoestot RR E thus current is (less than 50 μA which is ) less than150 μA. Assumption: resistance of the human body is zero. ..…………………………………………………………………………………………. ..…………………………………………………………………………………… [2] (iii) State and explain how the measured value of the resistance of the shoes will change if the voltmeter is not ideal. If the voltmeter is not ideal, the effective resistance of 1.00 MΩ resistor and voltmeter will be lower, and the potential difference across the 1.00 MΩ resistor and voltmeter will be lower. The measured value of resistance will be higher . [2]

River Valley High School Pg 5 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 [Turn over 4. The variation of current I with potential difference V across an electrical component X is shown below in Fig.4.1. Fig. 4.1 (a) Fig. 4.2 shows a battery, a potential divider and component X. Complete Fig. 4.2 to show a setup that can be used to obtain readings for Fig. 4.1. Include in your diagram any other relevant components and measuring instruments. Fig. 4.2 (accept ammeter in series with X) [2] (b) With reference to Fig. 4.1, describe how the resistance of X varies with the I / A V / V X A V

River Valley High School Pg 6 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 potential difference across it. As V increases, the ratio of I against V decreases, since R = V / I, hence the resistance increases. ..…………………………………………………………………………………… [2] (c) Component X is now connected across the terminal of a cell of e.m.f. 2.0 V with negligible internal resistance. Using Fig. 4.1, determine the resistance of X. From Fig 4.1, when V = 2.0 V, I = 2.4 A, RX = V / I = 2/ 2.4 = 0.83  Resistance of X = ……………  [2] (d) A fixed resistor of value 1.0  is connected in series with the cell in (c) and X. Using Fig. 4.1, or otherwise, determine the current in the circuit. Vx + (1) I = 2 Hence I = 2 - Vx A graph of I = 2 - Vx will intercept original graph at I = 1.3 A [3]

River Valley High School Pg 7 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016 [Turn over 5 (a) (i) Define the tesla. If a long straight conductor carrying a current of 1 amp is placed at right angles to a uniform magnetic field of flux density of 1 tesla, then the force per unit length on the conductor is 1 newton per metre. ..…………………………………………………………………………………… [1] (ii) Express the tesla in terms of the product of its base units. 1 T = 1 N / Am = kg m s2 / A m = kg s2 A1 base units = …………………………. [1] (b) Two long straight current -carrying conductors X and Y are placed parallel to each other. Conductor X carries a current of 2 A while conductor Y carries a current of 1 A. Both directions of currents are into the plane of the paper. (i) Sketch the magnetic flux pattern due to X and Y in Fig. 5.1 below. [2] [Asymmetry field lines, More field lines at X, Arrows correct directions] Fig. 5.1 (c) A third conductor Z with a current of 1 A into the plane of the paper is placed on the right of Y. Y is of equal distance from X and Z. Fig. 5.2 (i) Indicate with clear labelling on Fig. 5.2 the forces acting on Y. [1] [left arrow double in length compared to right arrow] X Y Z 1 A 2 A 1 A Force on Y due to X Force on Y due to Z

River Valley High School Pg 8 of 22 Year 6 H1 Physics 8866 Preliminary Examinations II 2016