GYSS 4E Physics Prelim P2 answer

1 The diagram shows a model car with a mass of 0.25 kg. The car is travelling at a constant speed of 1.70 m/s as it approaches the rough ramp. The average friction opposing the motion of the car down the ramp is 0.15 N. Assume air resistance is negligible. (a) Calculate the work done against friction as it moves down the rough ramp. work done = f x d = 0.15 x 0.42 = 0.0630 J [1] (b) Calculate (i) the loss in gravitational potential energy as the car moves down the the ramp, Ep = 0.25 x 10 x 0.8 = 2.00 J [1] (ii) the speed of the car at the bottom of the rough ramp. Ek = 2 + (½ x 0.25 x 1.72) – 0.063 = 2.29825 [1] 2.29825= ½ x 0.25 x v2 v2 = 18.386 v = 4.29 m/s [1] (c) Draw a free body diagram of the other forces acting on the car when it moves down the ramp, labelling the forces acting on the car. [Total: 6] weight friction contact force [2] 0.80 m 0.42 m

2 Fig. 2.1 shows a lorry accelerating along a straight road. The driving force exerted on the lorry in the forward direction is D and the total backward force acting on the lorry is B. Fig. 2.1 The gravitational field strength is 10 N/kg. (a) Compare the magnitude of the forces D and B. Give a reason for your answer. Force D is greater than force B, so that the resultant force acting on the lorry is in the forward direction, causing it to accelerate forward. [1] (b) The lorry subsequently turns a corner at a constant speed of 12 m/s. (i) Express the speed of the lorry in km/h. 12 m/s = (12/1000)/(1/3600) = 43.2 km/h [1] (ii) State and explain whether the lorry is accelerating when it turns the corner. Since the direction of the lorry’s velocity changes as it turns the corner, there is a change in its velocity. Hence the lorry is accelerating, even though its speed is constant. [1] [Total: 3]

3 Fig. 3.1 shows a uniform plank of mass 5.0 kg and length 2.0 m resting horizontally on two trestles, P and Q. Fig. 3.1 Trestle Q exerts a force of 440 N on the plank when an object of mass 65.0 kg is placed at a distance, d, from P. The gravitational field strength, g = 10 N/kg. (a) Calculate the moment due to the weight of the plank. moment = 50 x 1 = 50 Nm [1] (b) State the principle of moment. For an object to be in equilibrium, the sum of clockwise moment about the pivot is equal to sum of anti-clockwise moment about the same pivot. [1] (c) Determine the distance d, of the object from P. sum of clockwise moment = sum of anti-clockwise moment (50 x 1) + (650 x d) = 440 x 2 [1] 5 + 650d = 880 650d = 830 d = 830/650 = 1.2769 [1] = 1.28 m [Total: 4] P Q d 65 kg W

4 (a) Fig. 4.1 shows a ray of light XY being directed at the surface AB of an irregular- shaped glass block ABCDE. Fig. 4.1 (i) Explain why the ray XY enters surface AB without bending. The light is travelling alone the normal and thus no refraction of light. [1] (ii) Determine the critical angle of the glass. critical angle = 44.0o [1] (iii) Calculate the speed of the light ray in the glass block. n = 1/(sin 44o) = 1.43956 = 1.44 (3 s.f.)- [1] n = c/v v = c/n = 3 x 108/1.43956 = 2.08 x 108 m/s [1] D A B C E X Y 46 110

(b) Fig. 4.2 shows how a thin converging lens L made of the same glass is used to produce a sharp image of an arrow that is twice the size of the illuminated object. In the space below, complete the diagram from the top of the object to show how the sharp image is formed. Fig. 4.2 [2] [Total: 8] 5 The diagram shows a negatively charged metallic sphere held with an insulating handle. When the sphere is brought towards a metal plate, the sensitive galvanometer registers a momentary deflection. (a) Explain why the galvanometer registered a momentary deflection when the charged sphere was brought near. The electrons from the metal plate is being repelled by the negatively charged sphere as like charges repel. [1] As the metal plate is earthed this will allows the electrons to move to the earth. This movement of electrons causes the deflection on the galvanometer. [1] (b) Draw on the above diagram, the electric field set up between the sphere and the plate when the sphere was brought near. [1] (c) Describe what would be observed if the charged sphere was held in hand and moved towards the metal plate. Explain your observation. There will be no deflection. [1] metal plate [1] sphere

The charged sphere will be discharged when held in hand as the sphere is being earthed through the hand. [1] [Total: 5] 6 The diagram shows an electrical circuit with different electrical components. The resistance of X is 2000 Ω and 400 Ω in dark and bright conditions respectively. (a) State the name of component X light dependent resistor [1] (b) When S1 and S2 are opened in a bright room, calculate (i) the effective resistance of the circuit, total resistance = [1/(80 + 400) + 1/30]-1 [1] = [1/480 + 1/80]-1 = 28.2353 = 28.2 Ω [1] (ii) the charge flowing through the battery in 2 minutes. Q = It = (12/28.2353) x (2 x 60) [1] = 50.9671 = 51.0 C [1] (c) When S1 and S2 are closed in a dark room, (i) calculate the power dissipated in X. power = V2/R = 122/2000 [1] = 144/2000 = 0.0720 W [1] A1 D C 80 Ω 12 V A2 E S1 60 Ω 30 Ω S2 X

(ii) describe what measurements are taken and how they are used to find the energy produced by the 30 Ω in 2 minutes. Measure the current flowing through the 30 Ω, the potential difference across it and the time taken [1] Energy produced can be found using the formula E = IVt. [1] [Total 9] 7 An electric kettle consists of two heating elements as shown in the diagram below. The heating elements can be connected to the electrical mains supply of 240 V in various ways so that the heating power can be varied. (a) Complete the circuit so that the heating power is the maximum and the kettle is safe to use. [2] (b) The maximum heating power of the electric kettle is 550 W. Determine the fuse rating for the kettle. P = IV 550 = I x 240 I = 550/240 = 2.292 A = 2.29 A Thus fuse rating = 3.0 A [1] (c) Draw, on the above diagram, the correct position for the fuse and switch. Explain your answer. [The fuse and the switch should be placed in the live wire] [1] In the event the fuse blow or the switch is opened. The appliance will be disconnected from the live wire. [1] [1] [1] – connection in series

(d) Electrical energy costs $0.27 per kWh. Calculate the cost of using the kettle when switched on for 40 minutes every day in one month (i.e. 30 days). total kWh = 550/1000 x 40/60 x 30 = 0.55 x 2/3 x 30 = 11 kWh [1] total cost = 11 x 0.27 = $ 2.97 [1] [Total: 7] 8 (a) The diagram shows a mechanical device. (i) State the name and function of