61. In the equation of virtual work, following force is neglected
(a) reaction of any smooth surface with which the body is in contact
(b) reaction of a rough surface of a body which rolls on it without slipping
(c) reaction at a point or an axis, fixed in space, around which a body is con-strained to turn
(d) all of the above
(e) none of the above.
62. If a suspended body is struck at the center of percussion, then the pressure on die axis passing through the point of suspension will be
(e) same as the force applied.
65. The resultant of the following three couples 20 kg force, 0.5 m arm, $ ve sense 30 kg force, 1 m arm, – ve sense 40 kg force, 0.25 m arm, + ve sense having arm of 0.5 m will be
(a) 20 kg, – ve sense
(b) 20 kg, + ve sense
(c) 10 kg, + ve sense
(d) 10 kg, – ve sense
(e) 45 kg, + ve sense.
68. Angle of friction is the
(a) angle between normal reaction and the resultant of normal reaction and the limiting friction
(b) ratio of limiting friction and normal reaction
(c) the ratio of minimum friction force to the friction force acting when the body is just about to move
(d) the ratio of minimum friction force to friction force acting when the body is in motion
(e) ratio of static and dynamic friction.
69. The coefficient of friction depends on
(a) area of contact
(b) shape of surfaces
(c) strength of surfaces
(d) nature of surface
(e) all of the above.
70. Least force required to draw a body up the inclined plane is W sin (plane inclination + friction angle) applied in the direction
(a) along the plane
(d) at an angle equal to the angle of friction to the inclined plane