PHYSICS Paper 2

Materials For this paper you must have: • a pencil and a ruler • a scientific calculator • a Data and Formulae Booklet • a protractor. Instructions • Use black ink or black ball-point pen. • Fill in the boxes at the top of this page. • Answer all questions. • You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. Time allowed: 2 hours • If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s). • Do all rough work in this book. Cross through any work you do not want to be marked. • Show all your working. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 85. • You are expected to use a scientific calculator where appropriate. • A Data and Formulae Booklet is provided as a loose insert. 7408/2 Section A Answer all questions in this section. Do not write outside the box 0 1 Figure 1 shows an electric steam iron. Figure 1 Water from a reservoir drips onto an electrically-heated metal plate. The water boils and steam escapes through holes in the metal plate. The electrical power of the heater inside the iron is 2.1 kW. Assume that all the energy from the heater is transferred to the metal plate. 0 1 . 1 The metal plate has a mass of 1.2 kg and is initially at a temperature of 20 °C. The heater is switched on. After a time t the metal plate reaches its working temperature of 125 °C. Calculate t. specific heat capacity of the metal = 450 J kg−1 K−1 [2 marks] t = s . The metal plate is maintained at its working temperature. Water at 20 °C drips continuously onto the metal plate. Steam at 100 °C emerges continuously from the iron. The maker claims that the iron can generate steam at a rate of 60 g min−1. Determine whether this claim is true. specific latent heat of vaporisation of water = 2.3  106 J kg−1 specific heat capacity of water = 4200 J kg−1 K−1 [3 marks] Do not write outside the box Turn over ► . In the kinetic theory model, it is assumed that there are many identical particles moving at random. State two other assumptions made in deriving the equation pV = 1 Nm (crms)2. 3 Do not write outside the box [2 marks] 1 2