Mechanical previous year question papers

8/10/2019 Mechanical previous year question papers

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UNIT- IV. GEARS

1. Two mating involutes spur gears of 20 pressure angle have a gear ratio of 2. The number

of teeth on the pinion of 20 and its speed is 250 revolutions per minute. The module pitch

of the teeth is 12 mm. If theaddendum on each wheel is such that the path of approach and

the path of recess on each side are half the maximum possible length each, Find:

(i) The addendum for pinion and gear wheel;

(ii)

The length of arc contact:

(iii) The maximum velocity of sliding during approach and recess. Assume pinion to

be driver.

2. In a reverted epicyclic train shown in Figure 14(b), the arm F carries two wheels A and D

and a compound wheel B-C. The wheel A meshes with wheel B and the wheel D meshes

with wheel C. The numbers of teeth on wheel A, D and C are 80, 48 and 72 respectively.

Find the speed and direction of wheel D and wheel A is fixed and arm F, makes 200

revolutions per minute clockwise.

3. Figure 1 shows a compound epi-cyclic train employee to run a winch drum. Input shaft

keyed to Gear 1 is driven at 40 rpm clockwise and gear 4 is fixed. Number of teeth on each

gear wheel is given in figure. Determine the speed and direction of the drum.


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4. A pair of involute spur gears with 16 pressure angle and pitch of module 6 mm is in mesh.

The number of teeth on pinion is 16 and its rotational speed is 240 rpm. When the gear

ratio is 1.75, find in order that the interference is just avoided,

(i) Addendum on the pinion and gear wheel

(ii) The length of path of contact and

(iii) The maximum velocity of sliding of teeth on either side of the pitch point.

5.

In a sun and planet type epicyclic gear train, the pitch circle diameter of the annulus is to be

approximately 324 mm and the module 6 mm. When the annulus is stationary, the three

armed spider makes one revolution for every five revolutions of the sun wheel S.

Determine the number of teeth for all the wheel and exact pitch circle diameter of annulus.

6. A Gear wheel with 48 teeth of involute profile meshes with another wheel of 30 teeth. If

the module is 5 mm and a standard addendum of one module is used. Find

(i) The length of path of contact.

(ii)

The length of arc of contact.(iii) Contact ratio.

7. An epicyclic gear train consists of internal gear A, a pinion B and a wheel C. The wheel C

is concentric with A The pinion B is carried on an arm and gears with A and number of

teeth A and C are 96 and 48 respectively, determine the speeds of B and C when the gear A

is fixed

8. An epicyclic gear train consists of a sun wheel S, a stationary internal gear E and three

identical planet wheels P carried on a star shaped planet carrier C. The size of different

toothed wheels are such that the planet carrier C rotates at 1/5th of the speed of the sun

wheel S. The minimum number of teeth on any wheel is 16.The driving torque on the sun

wheel is 100 N-m. Determine number of teeth on different wheels of the train and the

torque necessary to keep the internal gear stationary.

9. Two gears in mesh have a module of 8 mm and a pressure angle of 20. The larger gear has

57 while the pinion has 23 teeth. If the addenda on pinion and gear wheel are equal to one

module, find

(i) The number of pairs of teeth in contact

(ii) The angle of action of the pinion and the gear wheel

(iii) The ratio of the sliding to rolling velocity at

(1)The beginning of contact

(2)The pitch point

(3)The end of contact.

10.In an epicyclic gear train shown in Fig. 14(b), the input S has 24 teeth; P and C constitute a

compound planet having 30 and 18 teeth respectively. If all the gears are of the same pitch,find the speed ratio of the gear train. Assume A to be fixed.


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11.

A Simple gear train consists of three gears, each mounted on separate shaft as shown in thefigure. The shafts are parallel. The gear 1 is the driver and the gear 3 is the follower. Gear 1

is rotating clockwise at a speed of 750 rpm. Number of teeth on gears 1, 2 and 3 are 30, 45

and 75 respectively. Determine Speed ratio of the gear train and Direction of rotation and

speed of rotation of follower.

12.The figure shows the planetary gear arrangement that has two inputs. Sun gear 2 rotates at

500 rpm and arm 6 rotates at 750 rpm both clockwise, as viewed from the left. Determinethe speed and direction of rotation of gear 5. Number of teeth (T) in various gears is shown

in the figure.


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13.An epicyclic train has a pinion A having 15 teeth, centrally located and rigidly connected to

shaft of driving motor. Another gear B having 20 teeth is gearing with A and also withannular fixed wheel D. Gear C is integral with B and meshes with another annular wheel E

which is keyed to the shaft of driven unit. The arm rotates about driving shaft and carries

compound gear B,C. Sketch the arrangement and determine speed of machine for a motor

speed of 1000 rpm. Also determine torque on machine shaft for a motor torque of 100 N-m.

14.Two mating gears have 20 and 40 involute teeth of module 10 mm and 20 pressure angle.

The addendum on each wheel is to be made of such a length that the line of contact on each

side of the pitch point has half the maximum possible length. Determine the addendum

height for each gear wheel, length of the path of contact, arc of contact and contact ratio.

UNIT-V. FRICTIONS

1. A screw-jack has a square thread of mean diameter 6 cm and pitch 0.8 cm. The co-efficient

of friction at the screw thread is 0.09. A load of 3 kN is to be lifted through 12 cm.

Determine the torque required and the work done in lifting the load through 12 cm. Find

the efficiency of the jack also.

2. A load of 25 kN is supported by a conical pivot with angle of cone as 120. The intensity of

pressure is not to exceed 350 kN/m2. The external radius is 2 times the internal radius. The

shaft is rotating at 180 revolutions per minute and co-efficient of friction is 0.05. Find the

power absorbed in friction assuming uniform pressure.

3. An open belt running over two pulleys 1.5 m and 1.0 m diameters connects two parallel

shafts 4.80 m apart. The initial tension in the belt when stationary is 3000N. If the smaller

pulley is rotating at 600 revolutions per minute and the coefficient of friction between the

belt and the pulley is 0.3, determine the power transmitted taking centrifugal tension intoaccount. The mass of the belt is given as 0.673 kg/length.

4. A clutch is required to transmit 10 kW at 3000 rpm. It is of single plate type, both sides

being effective. The coefficient of friction is 0.25 and the axial pressure is limited to 8.5 N/

cm2


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Determine the dimensions of the plate, assuming that the external diameter is 1.4

times the inner diameter.

5. A rope pulley with 10 ropes and peripheral speed of 1500 m/min transmits 100 kW. The

angle embraced by each rope is 180, the angle of groove is 40 and the coefficient of

friction is 0.2. Find the tensions on the tight and slack sides of the rope, allowing for

centrifugal tension. The weight of each rope is 6 N per metre run.

6. A leather belt transmit 10 kW from a motor running at 600 rpm by an open belt drive. The

diameter of the driven pulley is 350 mm and the centre distance between the pulleys is 4 m.

The speed of the driven pulley is 180 rpm. The density of the belt material is 1.1 Mg/m3

and the maximum permissible stress in the belt material is not to exceed 2.5MPa. The

thickness of the belt is 12 mm and the co-efficient of friction between the belt and pulley

surface is 0.25. Determine the necessary width of the belt.

7.

A band brake acts on the 3/4th of the circumference of a drum of 450 mm diameter whichis keyed to the shaft. The band brake provides a braking torque of 225 N-m. One end of the

band is attached to a fulcrum pin of the lever and the other end to a pin I 00 mm from the

fulcrum. If the operating force is applied at 500 mm from the fulcrum and the co-efficient

of friction is 0.25. Determine the operating when the drum rotates in the (a) anticlockwise

direction and (ii) clockwise direction.

8. A car engine has its rated output of 30 kW at 3000 rpm. The clutch used is of single plate

type, having two active surfaces. The axial pressure is not to exceed 0.85 bar. The external

diameter of the friction plate is 1.25 times the internal diameter and the co-efficient of

friction is 0.3. Determine the dimensions of the friction plate and the axial force exerted by

the springs.

9. The pitch of 50 mm mean diameter threaded screw of a screw jack is 12.5 mm. The

coefficient of friction between the screw and the nut is 0.13. Determine the torque required

on the screw to raise the load of 25 kN, assuming the load to rotate with the screw.

Determine the ratio of the torque required to raise the load to the torque required to lower

the load and also the efficiency of the screw jack.

10.A single plate clutch, both sides are effective, is to be designed for an automotive vehicle

whose engine is rated to give 100 kW at 2400 rpm and maximum torque 500 N-m. The

outer diameter of the friction plate is 25% more than the inner diameter. The intensity of

pressure between the plates is not to exceed 0.07 N/mm2.The co-efficient of friction may be

assumed equal to 0.3. Calculate the dimensions of the friction plate.

11.A shaft rotating at 200 r.p.m drives another shaft at 300 r.p.m and transmits 6 KW through

a belt. The belt is 100 mm wide and 10 mm thick. The distance between the shafts is 4 m.the smaller pulley is 0.5m in diameter. Calculate the stress in the belt if it is

(i) an open belt drive and (ii) a cross belt drive. Take =0.3.


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12.The wheel base of the car is 3 meters and its centre of gravity is1.2 meters ahead the rear

axle and 0.75 m above the ground level. The coefficient of friction between the wheels and

the road is 0.5. Determine the maximum deceleration of the car when it moves on a level

road. If the braking force on all the wheels is the same and no wheel slip occurs.

13.The following data relate to a screw jack:

Pitch of the screw thread = 8 mm

Diameter of the screw = 40 mm

Coefficient of friction between screw and nut= 0.1

Load = 20 kNAssuming that the load rotates with the screw,Determine

(1)The ratio of torques required to raise and lower the load

(2)The efficiency of the machine.

14.A multi-plate disc clutch transmits 55 kW of power at 1800 rpm. Coefficient of friction for

the friction surfaces is 0 .1. Axial intensity of pressure is not to exceed 160 kN/m2. The

internal radius is 80 mm and is 0.7 times the external radius. Find the number of platesneeded to transmit the required torque.

15.A power of 60kW is transmitted by a multi plate clutch at 1500 rpm. Axial intensity of

pressure is not to exceed 0.15 N/mm2. Coefficient of friction for the friction surface is 0.15.

The external radius of friction surface is 120 mm. Also the external radius is equal to 1.25

times of internal radius. Determine the number of plates needed to transmit the required

power, if wear is uniform.

16.An effort of 200 N is required to just to move a certain body up an inclined plane of an

angle 15, the force acting parallel to the plane. If the angle of inclination of the plane is

made 20o, the effort required parallel to the plane is found to be 230N. Determine the

weight of the body and the coefficient of friction.

17.Pitch of 50 mm diameter threaded screw of a screw jack is 12.5 mm. Coefficient of friction

between screw and nut is 0.10. Determine the torque to raise a load of 25 kN rotating with

the screw. Also find the torque required to lower the load and efficiency of screw jack.

(ii) 100 kW is to be transmitted by a rope drive through a 160 cm diameter 45

grooved pulley running at 200 rpm. Angle of overlap is 140 and coefficient of

friction between pulley and rope is 0.25. Mass of rope is 0.7 Kg/m and it can

withstand a tension of 800 N. Considering centrifugal tension, find the following:

(1)Number of ropes required

(2)Initial tension in the rope.

18.A 10 kW engine develops a maximum torque of 100 N-m and is driving a car having a

single plate clutch of two active surfaces.Axial pressure is not to exceed 0.85 bar. External

diameter of friction plate is 1.25 times internal diameter. Assume uniform wear and

coefficient of friction = 0.3. Determine dimension of friction plate and axial force exerted

by the springs.

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Mechanical previous year question papers