civils mains 2013 MECHANICAL ENGINEERING Paper-I

Time Allowed: Three Hours

Maximum Marks: 250

QUESTION PAPER SPECIFIC INSTRUCTIONS

Please read each of the following instructions carefulIy before attempting questions.
There are EIGHT questions divided in Two Sections and printed both in HINDI and in ENGLISH.
Candidate has to attempt FIVE questions in all.
Question no. 1 and 5 are compulsory and out of the remaining, THREE are to be attempted choosing at least ONE from each section.
The number of marks carried by a question/part is indicated against it.
Answers must be written in the medium authorized in the Admission certificate which must be stated clearly on the cover of this Question-cum-Answer booklet in the space provided. No marks will be given for answers written in medium other than the authorized one. Wherever any assumptions are made for answering a question, they must be clearly indicated.
Diagrams/Figures, wherever required, shall be drawn in the space provided for answering the question itself.
Unless otherwise mentioned, symbols and notations carry their usual standard meaning. Attempts of questions shall be counted in chronological order. Unless struck off, attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the answer book must be clearly struck off.

SECTION-A

Q. In the Figure shown below, block C has a mass of 50 kg and is confined between two walls by smooth rollers. If the block rests on the top of the 40 kg spool, determine the required coefficient of static friction at A and B so that the spool slips at A and B when the magnitude of applied force P is increased to 300 <img src='./qimages/188-1a.jpg'> 10

Q. In the Figure shown, a plate is supported at three positions, Band C. A is the ball and socket support, B is the roller support and CD is the cord. Determine the components of reactions at A and B and tension in cord CD. <img src='./qimages/188-1b.jpg'> 10

Q. The bending moment diagram for a simply supported beam AB is shown in Fig. below. Sketch the loading diagram and S.F. diagram of the beam. <img src='./qimages/188-1c.jpg'> 10
Q. Distinguish clearly the function of a flywheel used in I.e. Engines and in mechanical punching presses. For the same power output, why flywheels of multi-cylinder inline engines are relatively smaller than that of single cylinder engine 10
Q. Differentiate between annealing, and tempering. Mark the processes on a TIT diagram and bring out the transformations that take place during the process. 10

Q. A compound pendulum of mass 27 kg is suspended from a pivot, such that the distance of pivot from the mass centre of pendulum is 380 mm. When the pendulum swings about its pivot with small oscillation, the period of oscillation is 1.60 second. If the pendulum is now made to swing with amplitude of 45° on each side of the vertical, find the force exerted on the pivot at the extremity of the swing. 25

Q. A simply supported beam of 3 m span is subjected to loads as shown below. The beam is of I-section and all its dimensions are shown in mm. Determine the principal stresses at point D in the web. This section is located at a distance of 1 m from the right hand support of the beam.<br><br> <img src='./qimages/188-2b.jpg'> 25

I-Section

Q. In a loaded component principal stresses at a point are 130 MPa and 30 MPa. Using Mohr's stress circle, determine the state of stress at the point with respect to axes and which are inclined to and cr2 (principal stress) axes at 300 each in anticlockwise direction. Also determine principal strains at the point. Take E 200 OPa and G 80 GPa. 20

Q. The mass of an electric motor is 100 kg. The mass of the armature alone is 30 kg and its centre of gravity lies 0.5 mm from the axis of rotation. The motor is mounted on five springs of negligible damping and the force transmitted to the floor is one-eleventh of the applied force. Assuming mass of the motor is equally distributed among the five springs, determine the stiffness of each spring dynamic force transmitted to the floor. The motor is operating at a speed of 1400 rpm. 10

Q. In the epicyclic gear train shown in the Figure, SI is the driver, Az is connected to output. Al and Az are annulus gears, and and Sz are external gears, in which Sz is fixed gear, Given the tooth numbers of gears are Sj 40, Sz 30, 120 and A2 100, determine the velocity ratio of the co-axial shafts, Determine also the magnitude and direction of the torque required to fix if a ,torque of 300 N-m is applied in a clockwise direction to <img src='./qimages/188-3c.jpg'>

Q. In the figure shown, the end A of a bar AB, is constrained to move along vertical path AD and the bar passes through a swivel bearing pivoted at When A has a velocity of 3 m/s towards D and an acceleration of 25 m/s2 in the opposite direction, determine velocity and acceleration of sliding of bar thr01,;gh the swivel, 'angular velocity and angular acceleration of AB, <img src='./qimages/188-4a2.jpg'> 25

Q. 4(b)What are the desirable properties while selecting a tool material for metal-cutting applications? Compare HSS and ceramic tools with regard to their application in high speed machining. 15

Q.4(c)What are composite materials? Enumerate the advantages and limitations of the use of composites as engineering materials.10
SECTION-B

Q.5(a)What is ·underlying philosophy behind JIT systems? BrieflY describe the characteristics of JIT systems. 10

Q5(b)List the basic principles of plant layout.10

Q. Bars of length 20.05/19.95 mm are in stock. From each, piece of 5.03/4.98 mm are cut. Determine the lengths of the remaining parts. 10
Q. A cup, of 50 mm diameter and 100 mm height, is to be drawn from low carbon steel sheet. Neglecting the influence of thickness and corner radii(i) calculate the blank diameter
decide whether it can be drawn in a single draw, if maximum reduction permitted is 40%. 10

Q. For a machined surface, show macro- and micro-irregularities. What are their causes? What are the various measures of surface finish Explain any three of them. 10

Q. An open loop type NC machine has a stepper motor with a step of 0.9 degree. The lead screw of the machine is of 4 mm pitch. If the tool has to be moved by 2.87 mm, how many pulses will have to be fed? If the motor is rotating at 15 r.p.m., what is the pulse frequency and the feed rate of the machining operation ?10

Q. The process capability of machines manufacturing holes and shafts 15 ±0.24 min. The a5senibly requirements for the hole/shaft, of nominal dimension 20.00 mm, are of clearance between 0.04 and 0.08 mm. Devise the complete scheme (state what it is so that satisfactory assemblies are made. <img src='./qimages/188-6b.jpg'> <img src='./qimages/188-6b1.jpg'>

Q. Sketch the set-up for spot welding showing details of power input and electrodes: Draw the force/time and current/time diagrams. Explain how heating takes place. Indicate order of magnitude of current, voltage and time. How projection welding is different from spot welding? 10

Q. The following table gives the monthwise actual demand of units of some product: <img src='./qimages/188-6d.jpg'> The forecasted demand for the month of March was 400 units. The firm uses exponential smoothing method with smoothing factor 0.2 to forecast demand. Calculate the tracking signal for the model. Comment on the smoothing factor. 20

Q. An assembly line is to produce 40 microwave ovens an hour. The relevant data for the work elements involved in assembly are given below <img src='./qimages/188-7a.jpg'> Draw the precedence diagram. Design a balanced assembly line. Calculate idle time, efficiency, and balance delay. What can be the maximum output from this assembly line? 25

Q. How is the domestic kitchen gas cylinder manufactured? State the raw material, its shape and the processes involved. 10

Q. A manufacturer carries stock of an item with an annual demand of 30,000 units. The setup cost and holding cost are not known precisely, though they vary between 100 I and 150 1. Calculate EOQ in both conditions. How sensitive is the optimal Q to sth ratio? If slh doubles or triples, what happens to economic order quantity 15


Q. A special screw is being produced on a machine. The diameter of screw is critical and the process is to be controlled. Twelve samples of four screws each are drawn chronologically and inspected. The data is tabulated below <img src='./qimages/188-8a.jpg'>
What is the principle of LBM(Laser Beam Meachining)?Draw a sketch and name the salient elements used in LBM. 15

Q.8(c)Determine the optimum speed, for minimum cost, for a machining operation. The data is as follows: <img src='./qimages/188-8c.jpg'>