Flat Belt - Mechanical Technology - Mechanics - Exam, Exams of Mechanical Engineering

Download Flat Belt - Mechanical Technology - Mechanics - Exam and more Exams Mechanical Engineering in PDF only on Docsity! Cork Institute of Technology Bachelor of Engineering in Mechanical Engineering- Award (EMECH_7_Y3) Summer 2008 Mechanics of Machines (Time: 3 Hours) Instructions Answer FOUR questions. All questions carry equal marks. Examiners: Mr. A. Bateman Dr. P. Delassus Dr. F. S. Murphy Q1. (a) Show that for a flat belt experiencing the centrifugal effect: T1 −mv 2 T2 −mv 2 = e µθ where m = mass per unit length of the belt material and v = belt velocity. (10 marks) (b) A belt transmits 20 horsepower from a pulley 0.9 m diameter, which runs at 300 rev/min. The angle of embrace of the belt and pulley is 160° and the coefficient of friction between belt and pulley is 0.25. The belt is 6.4 mm thick and has a density of 1107.3 kg/m3. Determine the minimum belt width for a maximum belt stress of 2 MPa. (15 marks) (1 horsepower = 746 watts) Q2. A motor vehicle has a mass of 1400 kg. The wheel radius is 0.3 m. The vehicle is equipped with four disc brakes, each comprising a circular disc attached to the wheel axle, upon which friction pads press from both sides at a mean radius of 0.11 m as shown in Figure (Question 2). The ‘active’ pad is actuated by a pressure cylinder of diameter 20 2 mm. The maximum pressure in the cylinder is 80 MPa. The friction coefficient between disc and pads is 0.1. Figure (Question 2) Assume equal effective braking on all four wheels and that the wheels do not skid. The vehicle is traveling at 30 m/s on a straight level road. Average wind resistance is 650 N. (a) Calculate the least distance in which the vehicle can be brought to rest. (15 marks) (b) Calculate the least distance in which the vehicle can be brought to rest when travelling down a hill of 1 in 10, the other conditions remaining the same. (10 marks) Q3. (a) A helical spring is attached at one end to a rigid support and has a mass M at its free end. The free end of the spring is connected to a dashpot so that, as the mass vibrates vertically, the resistance of the fluid in the dashpot opposes the motion of the mass. With regard to this spring mass system, describe with sketches the three cases of (i) over- damping (ii) critical-damping (iii) under-damping. (10 mark (b) A spring-mass-damper system has a stiffness k = 56 kN/m and mass m = 40kg. The actual damping provided is 20 percent of critical. Determine the value of the logarithmic decrement. (15 marks)