50. The following statement is one of the laws of Dynamic friction
A. The force of friction always acts in a direction opposite to that in which a body is moving
B. The magnitude of the kinetic friction bears a constant ratio to the normal reaction between two surfaces. The ratio being slightly less than that in the case of limiting friction
C. For moderate speeds the force of friction remains constant but decreases slightly with the increase of speed
D. all the above.
51. The angle which an inclined surface makes with the horiontal when a body placed on it is on the point of moving down, is called
A. angle of repose
B. angle of friction
C. angle of inclination
D. none of these.
52. Which one of the following statements is true ?
A. The tangent of the angle of friction is equal to coefficeint of friction
B. The angle of repose is equal to angle of friction
C. The tangent of the angle of repose is equal to coefficient of friction
D. All the above.
53. On a ladder resisting on a smooth ground and leaning against a rough vertical wall, the force of friction acts
A. towards the wall at its upper end
B. away from the wall at its upper end
C. upwards at its upper end
D. downwards at its upper end
54. On a ladder resting on a rough ground and leaning against a smooth vertical wall, the force of friction acts
A. downwards at its upper end
B. upwards at its upper end
C. perpendicular to the wall at its upper end
D. zero at its upper end
55. A block of weight 50 kg is placed on a horizontal plane. When a horizontal force of 18 kg is applied, the block is just on the point of motion. The angle of friction is
56. The velocity of a moving body, is
A. a vector quantity
B. a scalar quantity
C. a constant quantity
D. none of these.
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