Theory of Machine objective type questions/Multiple choice questions
Q51. For calculating the friction power for bearing, the assumptions made in practice are
(a) the rate of wearing at the surface is uniform
(b) the rubbing velocity is constant
(c) the pressure intensity is uniform
(d) (a) and (c) only.
Q52. In case of flat pivot bearing, the frictional torque transmitted for uniform pressure as compared to the frictional torque transmitted for uniform wear
(a) is more
(b) is less
(c) is constant
(d) may be more or less.
Q53. Choose the wrong statement
(a) The frictional torque transmitted by a shaft Fitted with a large number of collars is the same as transmitted by a shaft with one collar.
(b) The frictional force for uniform pressure, in case of a flat pivot bearing, can be assumed to be acting at a distance of two-thirds of the radius of the shaft from the axis of shaft.
(c) When horse power lost in friction is to be determined, uniform pressure is assumed for safe design of bearing.
(d) The frictional force for uniform pressure, in case of a flat collar pivot bearing, can be assumed to be acting at a distance of half of the sum of internal and external radii of the shaft.
Q54. A thrust bearing, having collars of external and internal diameters as 40 cm and 20 cm respectively, carries an axial load of 3000 kgf. The co-efficient of friction is 0.09 and shaft runs at 420 r.p.m. The horse power lost in friction is to be determined. The corresponding
value of friction torque would be
(a) 40.5 kgf-m
(b) 42 kgf-m
(c) 45.0 kgf-m
(d) 48.5 kgf-m.
Q55. Which of the following is an example of friction clutch?
(a) disc clutch
(b) cone clutch
(c) centrifugal clutch
(d) all of the above
Q56. When a journal is rotating in its bearing, the resultant of the normal force (RN) and frictional force (μRN)
(a) passes through the centre of the journal
(b) is tangent to the circle of the journal at the point of contact
(c) is tangent to a small circle of radius r × sin φ where φ = tan-1 μ.
(d) none of the above.
Q57. Friction circle in case of journal bearing is
(a) the circle of the journal
(b) the circle to which resultant force F is tangent
(c) the circle which is having radius equal to μ × R where R is the radius of the journal
(d) both (b) and (c)
Q58. The radius of friction circle increases
(a) with the increase of load
(b) with the increase of radius of journal
(c) with the increase of co-efficient of sliding friction
(d) (b) and (c) only.
Q59. Choose the wrong statement
(a) Angle of friction is the angle made by the normal reaction with the resultant of normal reaction and force of friction.
(b) Static frictions is more than dynamic friction.
(c) Limiting friction is the maximum frictional force, which comes into play when a body just begins to slide over the surface of other body.
(d) None of the above.
Q60. The tension caused by centrifugal force on the belts
(a) increases power transmission
(b) decreases power transmission
(c) does not affect power transmission
(d) none of the above.
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