9702_w07_qp_2
A paper of Physics, 9702
Questions:
7
Year:
2007
Paper:
2
Variant:
0
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2
Use A girl G is riding a bicycle at a constant velocity of 3.5 m s–1. At time t = 0, she passes a boy B sitting on a bicycle that is stationary, as illustrated in . B G t = 0 3.5 m s–1 At time t = 0, the boy sets off to catch up with the girl. He accelerates uniformly from time t = 0 until he reaches a speed of 5.6 m s–1 in a time of 5.0 s. He then continues at a constant speed of 5.6 m s–1. At time t = T, the boy catches up with the girl. T is measured in seconds. State, in terms of T, the distance moved by the girl before the boy catches up with her. distance = m For the boy, determine the distance moved during his acceleration, distance = m the distance moved during the time that he is moving at constant speed. Give your answer in terms of T. distance = m Examiner’s Use Use your answers in and to determine the time T taken for the boy to catch up with the girl. T = s The boy and the bicycle have a combined mass of 67 kg. Calculate the force required to cause the acceleration of the boy. force = N At a speed of 4.5 m s–1, the total resistive force acting on the boy and bicycle is 23 N. Determine the output power of the boy’s legs at this speed. power = W
2. Kinematics  →  2.1. Equations of motion
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3
Use Define potential energy. Distinguish between gravitational potential energy and elastic potential energy. gravitational potential energy elastic potential energy A small sphere of mass 51 g is suspended by a light inextensible string from a fixed point P. The centre of the sphere is 61 cm vertically below point P, as shown in . 18° 61 cm P sphere, mass 51g The sphere is moved to one side, keeping the string taut, so that the string makes an angle of 18° with the vertical. Calculate the gain in gravitational potential energy of the sphere, gain = ……………………… J Examiner’s Use the moment of the weight of the sphere about point P. moment = N m
5. Work, energy and power  →  5.2. Gravitational potential energy and kinetic energy
13. Gravitational fields  →  13.4. Gravitational potential
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4
Use A sample of material in the form of a cylindrical rod has length L and uniform area of cross-section A. The rod undergoes an increasing tensile stress until it breaks. shows the variation with stress of the strain in the rod. 0.01 0.02 strain stress / 108 Pa breaking point State whether the material of the rod is ductile, brittle or polymeric. Determine the Young modulus of the material of the rod. Young modulus = Pa Examiner’s Use A second cylindrical rod of the same material has a spherical bubble in it, as illustrated in . cylindrical rod cross-sectional area 1.9 x 103 N 3.2 x 10–6 m2 1.9 x 103 N bubble The rod has an area of cross-section of 3.2 × 10–6 m2 and is stretched by forces of magnitude 1.9 × 103 N. By reference to , calculate the maximum area of cross-section of the bubble such that the rod does not break. area = m2 A straight rod of the same material is bent as shown in . Suggest why a thin rod can bend more than a thick rod without breaking.
6. Deformation of solids  →  6.1. Stress and strain
6. Deformation of solids  →  6.2. Elastic and plastic behaviour
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5
Use shows the variation with time t of the displacement y of a wave W as it passes a point P. The wave has intensity I. y t wave W A second wave X of the same frequency as wave W also passes point P. This wave has intensity  I. The phase difference between the two waves is 60°. On , sketch the variation with time t of the displacement y of wave X. In a double-slit interference experiment using light of wavelength 540 nm, the separation of the slits is 0.700 mm. The fringes are viewed on a screen at a distance of 2.75 m from the double slit, as illustrated in (not to scale). coherent light wavelength 540 nm 0.700 mm 2.75 m screen Examiner’s Use Calculate the separation of the fringes observed on the screen. separation = mm State the effect, if any, on the appearance of the fringes observed on the screen when the following changes are made, separately, to the double-slit arrangement in . The width of each slit is increased but the separation remains constant. The separation of the slits is increased.
8. Superposition  →  8.3. Interference
8. Superposition  →  8.2. Diffraction
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6
Use An electric shower unit is to be fitted in a house. The shower is rated as 10.5 kW, 230 V. The shower unit is connected to the 230 V mains supply by a cable of length 16 m, as shown in . 16 m shower unit 10.5 kW 230 V cable copper wire copper wire 230 V supply Show that, for normal operation of the shower unit, the current is approximately 46 A. The resistance of the two wires in the cable causes the potential difference across the shower unit to be reduced. The potential difference across the shower unit must not be less than 225 V. The wires in the cable are made of copper of resistivity 1.8 × 10–8 Ω m. Assuming that the current in the wires is 46 A, calculate the maximum resistance of the cable, resistance = Ω Examiner’s Use the minimum area of cross-section of each wire in the cable. area = m2 Connecting the shower unit to the mains supply by means of a cable having wires with too small a cross-sectional area would significantly reduce the power output of the shower unit. Assuming that the shower is operating at 210 V, rather than 230 V, and that its resistance is unchanged, determine the ratio power dissipated by shower unit at 210 V power dissipated by shower unit at 230 V . ratio = Suggest and explain one further disadvantage of using wires of small cross-sectional area in the cable.
9. Electricity  →  9.3. Resistance and resistivity
9. Electricity  →  9.2. Potential difference and power
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