661. On the ladder resting on the ground and leaning against a smooth vertical wall, the force of friction will be
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

662. Pick up wrong statement about friction force for dry surfaces. Friction force is
A.Proportional to normal load between the surfaces
B.Dependent on the materials of contact surface
C.Proportional to velocity of sliding
D.Independent of the area of contact Surface

663. The escape velocity from the surface of the earth is approximately equal to
A.9.81 km/sec
B.11.2 km/sec
C.14 km/sec
D.22 km/sec

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

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

666. 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

667. 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

668. 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 ?. 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

669. The algebraic sum of moments of the forces forming couple about any point in their plane is
A.Equal to the moment of the couple
B.Constant
C.Both of above are correct
D.Both of above are wrong

670. hoose the wrong statement?
A. Viscosity of a fluid is that property which determines the amount of its resistance to a shearing force
B. Viscosity is due primarily to interaction between fluid molecules
C. Viscosity of liquids decreases with in-crease in temperature
D. Viscosity of liquids is appreciably affected by change in pressure
E. Viscosity is expressed as poise, stoke, or saybolt seconds

NOTE
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PLEASE COMMENT WITH CORRECT ANSWER AND ITS DETAIL EXPLANATION IN COMMENT BOX.
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