8/2/2019 12-05 Mechanics of Machines-I (ME)

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MEHRAN UNIVERSITY OF ENGINEERING ANDTECHNOLOGY,JAMSHORO.

FIRST TERM SECOND YEAR (3RD TERM) B.E.(MECHANICAL)REGULAR EXAMINATION 2005 OF 04-BATCH UNDER EXTERNAL

SYSTEM.

Date: 12-05-2005. Time Allowed: 03 Hours.

Max:Marks-80.NOTE: ATTEMPT ANY FIVE QUESTIONS. ALL QUESTIONS CARRY EQUALMARKS.

Q.Nos.

1. Derive an expression for the ratio of shafts velocities for Hooks joint.Two shafts are connected by Hooks joint. The driving shaft revolves uniformly at 500 rpm.

If the total permissible variation in speed of driven shaft is not to exceed 6% of the mean

speed find, the greatest permissible angle between the centerlines of the shafts.

2. In a screw jack, the helix angle of a thread is and the angle of friction is . Show that its

efficiency is maximum, when 2 = (90o- ).

A 150mm diameter valve against which the steam pressure of 2MN/m2 is acting, is closed by

means of square threaded screw 50mm in external diameter with 6mm pitch and coefficientof the friction 0.12, find the torque required to turn the handle.

3. Derive an expression for the friction moment for a flat collar bearing in terms of the inner

radius r1 outer radius r2, axial thrust W and coefficient of friction . Assume uniform

intensity of pressure. A thrust shaft of a ship has 6 collars of 550mm external diameter and280mm internal diameter. The total thrust from the propeller is 80KN. If the coefficient of

friction is 0.12 and speed of the engine 90r.p.m. Find the power absorbed in friction at the

thrust block, assuming uniform pressure.

4. It is stated that the speed at which the belt should run to transmit maximum power is that at

which the maximum tension is three times the centrifugal tension in the belt.

Prove the statementPower is transmitted using V-belt drive. The included angle of V-groove is 30o. The belt is

20mm deep and 20mm wide. If the mass of the belt is 0.35Kg/m length and maximum stress

is 1.4 M pa. Determine maximum power transmitted when angle of lap is 140o, =0.15.

5. Show that involute tooth profile satisfies law of gearing.

Two mating gears have 20 and 40 involute teeth of module 10mm and 20o pressure angle. Ifthe addendum on each wheel is such that the path of contact is maximum and interference is

just avoided find the addendum for each gear, path of contact, arc of contact and contact ratio.

6. Obtain an expression for the length of a belt in a cross belt drive.

Find the power transmitted by a belt running over a pulley of 550mm diameter at 180 rpm.

The co-efficient of friction between the belt and the pulley is 0.25, angle of lap 160o and

maximum tension in the belt is 2200N.

7. Name and define different types of gear trains.

A planetary gear train shown in the fig, the arm rotates 200rpm in counter clockwise directionand the sun gear rotates 100rpm clockwise. Find the speed and direction of rotation of

internal gear.

8. Describe with the help of a neat sketch the principles of operation of an internal expandingshoe brake. Derive an expression for the braking torque.

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