1. In a crank and slotted lever type quick return mechanism, the link moves with an angular velocity of 20 rad/s, while the slider moves with the linear velocity of 1.5 m/s. The magnitude and direction of Coriolis component of acceleration with respect to angular velocity are
a) 30 m/s2 and direction is such as to rotate slider velocity in the same sense as the angular velocity
b) 30 m/s2 and direction is such as to rotate slider velocity in the opposite sense as the angular velocity
c) 60 m/s2 and direction is such as to rotate slider velocity in the same sense as the angular velocity
d) 60 m/s2 and direction is such as to rotate slider velocity in the opposite sense as the angular velocity.
Explanation: Magnitude of Coriolis acceleration = 2Vω
= 2 x 1.5 x 20
= 60 m/s2
Rotate the link in direction of rotation and see the direction of linear velocity that will be direction of Coriolis acceleration.
2. Which of the following are associated with Ackerman steering mechanism used in automobiles?
1. Has both sliding and turning pairs
2. Less friction and hence long life
3. Mechanically correct in all positions
4. Mathematically not accurate except in three positions.
5. Has only turning pairs 6. Controls movement of two front wheels
a) 2, 4, 5 and 6
b) 1, 2, 3 and 6
c) 2, 3, 5 and 6
d) 1, 2, 3 and 5
Explanation: Ackerman steering mechanism has no sliding mechanism & not suitable for all the positions.
3. The crankshaft of reciprocating engine having a 20 cm crank and 100 cm connecting rod rotates at 210 r.p.m. When the crank angle is 45o, the velocity of piston is nearly
a) 1.8m/s
b) 1.9m/s
c) 3.5m/s
d) 19m/s
Explanation: Vp = ωr(sinϴ + sin2ϴ/2n)
ω = 2пN/60 = 21.98rad/sec
r = 6.2m
n = l/r = 100/20 = 5
therefore, Vp = 21.980 x 0.2(sin45o + sin90o/2 x 5)
= 3.5m/sec.
4. A single slider crank chain is a _______
a) 4-link mechanism
b) 3-link mechanism
c) 2-link mechanism
d) 6-link mechanism
Explanation: A single slider crank chain is a four link mechanism, any four link mechanisms has 4 links inclusive of higher and lower pairs.
5. Bull engine is an inversion of single slider crank chain.
a) True
b) False
Explanation: In a bull engine the inversion is obtained by fixing the cylinder, thus it is an inversion of a single slider crank chain.
6. Find the ratio of the time of cutting to the time of return stroke from the following information: A crank and slotted lever mechanism used in a shaper has a centre distance of 0.300 m between the centre of oscillation of the slotted lever and the centre of rotation of the crank. The radius of the crank is 0.120 m.
a) 1.72
b) 1.65
c) 1.81
d) 1.79
Explanation: We know that time of cutting stroke to the time of return stroke is given by
360-α/ α
Using trigonometric ratios we find that α =132.8°
therefore, Ratio = 1.72.
7. Find the inclination of the slotted bar with the vertical in degrees in the extreme position from the following information: In a crank and slotted lever quick return motion mechanism, the distance between the fixed centres is 0.240 m and the length of the driving crank is 0.120 m.
a) 30
b) 45
c) 60
d) 75
Explanation: In a crank and slotted lever mechanism, symmetry can be observed. Using this symmetry and trigonometric ratios we find that
angle = 30 degrees.
8. Find the ratio of the time of cutting to the time of return stroke from the following information: In a crank and slotted lever quick return motion mechanism, the distance between the fixed centres is 0.240 m and the length of the driving crank is 0.120 m.
a) 3
b) 4.5
c) 3.2
d) 2
Explanation: In a crank and slotted lever mechanism, symmetry can be observed. Using this symmetry and trigonometric ratios we find that vertical inclination of slotted bar is
angle = 30 degrees.
now 90- α/2 = 30
α=120 degrees
therefore ratio = 2.
9. Find the length of stroke if the length of the slotted bar is 0.45m and LOS passes through the free end of the lever. Length of driving crank = 0.12m, distance between fixe centres = 0.24m. Crank and slotted lever quick return motion mechanism.
a) 450mm
b) 400mm
c) 500mm
d) 475mm
Explanation: We know that length of stroke is:
2x450xsin(90-α/2)
α=120 degrees,
therefore
length = 450mm.
10. Which of the following mechanism is mostly used in shaping and slotting machines?
a) Whitworth quick return motion mechanism
b) Bull engine
c) Crank and slotted lever quick return motion mechanism
d) Gnome engine
Explanation: Whitworth quick return motion mechanism is mostly used in shaping and slotting machines, as in this mechanism a turning pair is fixed and the driving crank rotates at a uniform speed.