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The details of the semester 2 examinations for the mechanical and biomedical engineering course in the academic year 2009/2010. It includes the exam codes, modules, and papers related to the exams. The document also provides instructions for answering specific questions, the duration of the exams, and the required materials. The questions cover various topics such as design-build-test projects, material selection, and engineering mechanics.
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Exam Code(s) 1 BM, 1 BG, 1BN, 1BP, 1BEI, 1BEE, 1BSE, 1EG Exam(s) 1 st Engineering (Mechanical, Biomedical, Electronic, Electronic and Computer, Sports and Exercise, Engineering Innovation – Electronic, Energy Systems, Undenominated) Module Code(s) ME Module(s) Fundamentals of Mechanical Engineering Paper No. Repeat Paper External Examiner(s) Prof. Noel O’Dowd Internal Examiner(s) Prof. Sean Leen, Dr. Nathan Quinlan * Instructions: Answer Question 1 and 2 other questions. All questions carry equal marks. Duration 2 hours No. of Pages Department(s) Mechanical and Biomedical Engineering Course Co-ordinator(s) Dr. Nathan Quinlan Requirements: Statistical/ Log Tables yes Graph Paper yes Release to Library: yes
Question 1 is mandatory. 1 Answer the following questions about the design-build-test project you completed for this course. (a) Briefly describe your main contributions to your team’s analysis, design and development efforts. ( 8 ) (b) If you were to repeat this project, what would you do differently? In other words, what did you learn from the experience? (6) (c) Describe one example of how scientific and/or mathematical analysis played a part in your team’s design. (6)
3 An engine drives a winch through a gear train, as shown schematically in Figure Q 3. A cable wound on the winch is used to raise an object of mass 44 kg. The system is initially at rest. At time t = 1 s, shortly after the engine is started, the torque and speed are measured at the engine as 36 Nm and 80 rpm respectively. gear 2 (60 teeth) engine 4.4 kg gear 1 (18 teeth) Ø301 mm winch gear 2 (60 teeth) engine 44 kg gear 1 (18 teeth) Ø winch gear 2 (60 teeth) engine 4.4 kg gear 1 (18 teeth) Ø301 mm winch gear 2 (60 teeth) engine 44 kg gear 1 (18 teeth) Ø winch Figure Q3 Engine, gear train and winch. (a) Calculate the rotational speed of the winch and the torque on the winch at time t = 1 s. ( 6 ) (b) Calculate the linear speed and acceleration of the 44 - kg object at time t = 1 s. (6) (c) Some time later, the weight is observed to be rising at a steady speed (i.e. with zero acceleration) of 0.35 m/s. Calculate the speed of the engine and the torque on it in this condition. (8)
4 Figure Q4 shows a performance curve for a DC motor operating at constant voltage. The motor will be used to power a 800-kg vehicle with a gear ratio k (ratio of roadwheel speed to motor speed) of 1/4 and roadwheel diameter 430 mm. Throughout this question, neglect friction in all the vehicle’s internal mechanisms, and neglect aerodynamic effects. torque (Nm) speed (rpm) 0 1000 2000 3000 4000 5000 6000 100 80 60 40 20 0 torque (Nm) speed (rpm) 0 1000 2000 3000 4000 5000 6000 100 80 60 40 20 0 Figure Q4 Torque-speed characteristic of a DC motor operating at constant voltage. (a) Based on the shape of the curve in Figure Q4, derive an equation that gives motor torque as a function of rotational speed , maximum speed 0 and stall torque T 0. Hence derive a similar equation for power. ( 4 ) (b) Derive an equation for the equilibrium speed of the vehicle travelling up a slope at an angle to the horizontal, as a function of vehicle mass m , gear ratio k and roadwheel diameter d , as well as 0 and T 0. Sketch a graph of this function, showing speed as a function of gear ratio (with all other parameters constant). ( 6 ) (c) Calculate the roadwheel torque required to drive the vehicle at constant speed up a slope at an angle of 10 ° to the horizontal. (4) (d) Using the equation you derived in part (b) above, or otherwise, calculate the equilibrium speed of the vehicle when travelling up a slope at an angle of 10 ° to the horizontal. (6)