2025 AQA A-Level PHYSICS 7408/3BC Paper 3 Section B Engineering physics Question paper and Marking scheme Merged

2025 AQA A-Level PHYSICS 7408/3BC Paper 3 Section B Engineering physics Question paper and Marking scheme Merged Please write clearly in block capitals. Centre number Surname Forename(s) Candidate number Candidate signature I declare this is my own work. A-level PHYSICS Paper 3 Section B Engineering physics Tuesday 17 June 2025 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. Morning • Fill in the boxes at the top of this page. • Answer all questions. Time allowed: The total time for both sections of this paper is 2 hours. You are advised to spend approximately 50 minutes on this section. • You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. • 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 35. • You are expected to use a scientific calculator where appropriate. • A Data and Formulae Booklet is provided as a loose insert. For Examiner’s Use Question Mark 1 2 3 IB/M/Jun25/G4 4 TOTAL 2 Do not write outside the for more: IB/M/Jun25/7408/3BC Section B Answer all questions in this section. box The rotating part of an electric motor is called the rotor. Figure 1 shows an end view of a rotor turning clockwise due to a driving torque from the motor. In this question, the clockwise direction is treated as positive. Figure 1 Figure 2 The rotor can be brought to rest rapidly by reversing the electrical supply connections to the motor. Figure 2 shows the rotor at time t = 0 when the supply connections are reversed. The rotor then slows down due to a constant anticlockwise retarding torque so that it stops at time t = t1. The angular velocity of the rotor at t = 0 is 98.0 rad s−1 clockwise. The applied torque on the rotor at t = 0 is anticlockwise. The applied torque produces a constant angular acceleration of −303 rad s−2. Friction torque is negligible. . Determine t1. [2 marks] t1 = s 1 1 0 1 0 3 Do not write outside the for more: IB/M/Jun25/7408/3BC 2 3 The electrical supply remains connected and the rotor now accelerates uniformly anticlockwise with an acceleration of magnitude 303 rad s−2. At a later time t = t2, the angular velocity of the rotor is −120 rad s−1. box . Determine the number of anticlockwise revolutions made by the rotor between t1 and t2. [2 marks] number of revolutions = . The moment of inertia of the rotor about the axis of rotation is 9.60 × 10−2 kg m2. Calculate the angular impulse on the rotor between t = 0 and t2. [1 mark] angular impulse = N m s Question 1 continues on the next page Turn over ► 1 0 1 0 4 Do not write outside the for more: IB/M/Jun25/7408/3BC 4 . Another way of quickly stopping the motor is to use a disc brake. The motor is brought to rest by switching off the power supply and then forcing two brake pads against the disc. Figure 3 shows the two brake pads each applying a constant retarding force of 182 N to the disc. Figure 3 moment of inertia of rotor and disc about the axis of rotation = 0.101 kg m2 diameter of disc = 0.160 m diameter of pad = 22 mm Compare the angular deceleration produced by the disc brake system with the angular deceleration produced by reversing the electrical connections. box [3 marks] 8 1 0 5 Do not write outside the for more: IB/M/Jun25/7408/3BC 1 2gh 1 + A . The moment of inertia I of any rolling object about its axis of rotation is given by I = Amr2 where A is a constant that depends on the shape of the object m is the mass of the object r is the radius of the object. Figure 4 shows an object that starts from rest and rolls down a slope without slipping. Figure 4 The object falls a vertical distance h. It then has a linear velocity v and angular velocity ω. For a rolling object the linear velocity v of the centre of mass is related to the