64. For maximum range of a projectile, the angle of projection should be
A.30°
B.45°
C.60°
D.90°

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65. A projectile is fired at an angle θ to the vertical. Its horizontal range will be maximum when θ is
A.0°
B.30°
C.45°
D.60°

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66. Limiting force of friction is the
A.Tangent of angle between normal-reaction and the resultant of normal reaction and limiting friction
B.Ratio of limiting friction and normal reaction
C.The friction force acting when the body is just about to move
D.The friction force acting when the body is in motion

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67. Coulomb friction is the friction between
A.Bodies having relative motion
B.Two dry surfaces
C.Two lubricated surfaces
D.Solids and liquids

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68. Tangent of angle of friction is equal to
A.Kinetic friction
B.Limiting friction
C.Angle of repose
D.Coefficient of friction

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69. Kinetic friction is the
A.Tangent of angle between normal reaction and the resultant of normal reaction and the limiting friction
B.Ratio of limiting friction and normal reaction
C.The friction force acting when the body is just about to move
D.The friction force acting when the body is in motion

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70. A semi-circular disc rests on a horizontal surface with its top flat surface horizontal and circular portion touching down. The coefficient of friction between semicricular disc and horizontal surface is μ. This disc is to be pulled by a horizontal force applied at one edge and it always remains horizontal. When the disc is about to start moving, its top horizontal force will
A.Remain horizontal
B.Slant up towards direction of pull
C.Slant down towards direction of pull
D.Unpredictable

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