Friday, July 10, 2015

West Bengal University B.Tech Mechanical Engineering mechanism question paper of year 2013

University: West Bengal University
Course: B.Tech
Subject :  mechanism 

Year of  Question Paper : 2013
cs/b.tech/(me/pe/aue-new)/sem-4/me-402/2013
2013
mechanism
time allotted : 3 hours full marks : 70
the figures in the margin indicate full marks.
candidates are required to give their answers in their own words
as far as practicable
group-a
( multiple choice type questions )
1. choose the correct al e natives for the following : 10 × 1 = 10
i) in a four-link mech nism, the sum of the shortest and
the longest link is less than the sum of the other two
links. It will act as a drag-crank mechanism if
a) the longest link is fixed
b) the shortest link is fixed
c) the link opposite to the shortest link is fixed
d) any link adjacent to shortest link is fixed.
ii) in a four-link mechanism, torque transmitted to the
output link is maximum when transmission angle is
a) zero b) 180°
c) 45° d) 90°.
iii) minimum number of teeth in rack and pinion for
20° pair angle teeth is
a) 20 b) 18
c) 22 d) 24.
iv) the component of the acceleration, parallel to the
velocity of the particle, at the given instant is called
a) radial component b) tangential component
c) coriolis component d) none of these.
v) the train value of a gear train is
a) equal to velocity ratio of a gear train
b) reciprocal of velocity ratio f a gear train
c) always greater than nity
d) always less than unity.
vi) the pressure ngle of the cam ..................... with
increase in the base circle diameter.
a) decreases
b) increases
c) does not change
d) may decrease or increase.
vii) the ratio of tight side and slack side tension in a
V-belt is
a) sinaµ? e b) a
µ?
cos e
c) cosaµ? e d) a
µ?
sin e .
viii) a differential gear in automobile is used to
a) reduce the speed
b) help in turning
c) assist in changing speed
d) provide jerk-free movement of vehicle.
ix) the contact ratio of gears is always
a) more than one b) one
c) less than one d) zero.
x) which of the following is an inversion of double-slider
crank chain ?
a) whitworth quick return mechanism
b) reciprocating compressor
c) scotch Yoke
d) rotary engine
group-b
( short answer type questions )
answer any three of the following. 3 × 5 = 15
2. a) state the G uebler's criterion for ascertaining the
'degree of freedom' of a planar mechanism for turning
pairs only.
b) determine the degree of freedom (dof) of the
mechanism shown in the following figures : 2 + 3
3. the initial tension in a both deriver is found to be 400 newton and
the ratio of friction tension 1·7. the mass of both is
0·072 kg/m length. determine the following :
a) the velocity of belt for maximum power transmission
b) tension on the tight side of the belt when it is ready to
start
c) tension on the tight side of the belt when running at
maximum speed.
4. a) what is kutzback's criterion for degree of freedom of
plane mechanisms ?
b) in what way grubler's creation is different from it ?
3 + 2
5. a) how does whitworth quick return mechanism differ
from crank and slotted lever mechanism ?
b) indicate the 4 link mechanism.
indicate the type of each mechanism whether crank
rocker, double crank or double rocker. Dimensions are
in standard units 2 + 3

6. a) describe the fundamental law of gearing.
b) derive an expression for length of the path of contact in
a pair of involute gear teeth. 3 + 2
7. show that for the maximum power transmission condition
1/3rd of the maximum tension is absorbed as centrifugal
tension for a belt drive.

group-c
( long answer type questions )
answer any three of the following. 3 × 15 = 45
8. a) what is meant by interference in involute gear ?
explain. 2
b) two 14·5° involute spur gears mesh externally and give
a velocity ratio 3·5. Module is 4 mm and the addendum
is equal to 1·3 modules. If the pinion rotates at
320 rpm, determine —
i) the minimum number of teeth on each wheel to
avoid interference
ii) the number of pairs of teeth in conta t. 8
c) In an epicyclic gear the wh el a fixed to s1 has
30 teeth and rotates at 500 rpm. b gear with a and is
fixed rigidly to c, both being free to rotate on s2. the
wheel b, c and d have 50, 70 and 90 teeth respectively.
If d rotates at 80 rpm in a direction opposite to that of
a, find the speed of the shaft. 5
9. a) draw the profile of a cam operating a knife-edge follower
having a lift of 30 mm. The cam raises the follower with
shm for 150° of the rotation follower by a period of
dwell for 60°. The follower descends for the next 100°
rotation of the cam with uniform velocity, again followed
by a dwell period. The cam rotates at a uniform velocity
of 120 rpm and has a least radius of 20 mm. what will
be the maximum velocity and acceleration of the
follower during the lift and the return ? 7
b) a shaft which rotates at a constant speed of 160 rpm is
connected by belting in a parallel shaft 72 cm apart
which has to run at 60, 80 and 100 rpm. the smallest
pulley on the driver shaft is 4 cm in radius. determine
the remaining radii of the two stepped pulleys for (i) an
open belt, (ii) a cross belt. neglect belt thickness and
slip. 8
10. a) design a four link mechanism if the motions of the
input and output links are governed by a function
·51 = xy and x varies from 1 to 4. assume ? to vary from
30° to 120° and F from 60° to 130 . the length of the
fixed link is 30 mm. use chebychev spacing of accuracy
points.
b) a four-bar mechanism is required such that the input
and output angles are co-ordinate as given in the table.
synthesis the four bar mechanism
applying
freudenstein approach. 7 + 8
input link angle 30° 50° 80°
output link angle 0° 30° 60°
11. a) explain the terms 'function generation' and 'Path
generation'.
b) distinguish between higher pair and lower pair.
c) in a quick-return motion mechanism of crank and
slotted lever type, the ratio of maximum velocities is 2. If
the length of the stroke is 25 cm, find (i) the length of
the slotted lever, (ii) the ratio of times of cutting and
return stroke, and (iii) the maximum cutting velocity per
second, if the crank rotates at 30 rpm.
12. a) describe inversions of 4-bar chain giving suitable
sketches.
b) define the terms 'degrees of freedom' and 'constraint
motion' of a mechanism.
c) find out degrees of freedom of mechanism shown in
Fig. 4.
d) "slider crank mechanism is a special case of 4-bar
mechanism." Justify the statement.
4 + 4 + 3 + 4
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