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4

If a set of given forces are such that their free vectors build a closed polygon, then

A. The resultant force and resultant couple are always zero

B. The resultant force is zero but resultant couple is not zero

C. The resultant force is zero but resultant couple may not be zero

D. The resultant force and resultant couple both may not be zero

Correct Answer :

C. The resultant force is zero but resultant couple may not be zero


Related Questions

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4

A pilot flies a small plane in a vertical loop of radius r. At the top of its trajectory he experiences weightlessness. If the acceleration due to gravity is g, the speed of the plane at the top of its trajectory would be

A. Zero

B. Infinite

C. gr

D. 2gr

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4

The C.G. of the shaded area of the below figure from the x-axis is

A. a/4

B. 3a/4

C. 3b/10

D. 3a/10

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4

Two circular discs of same weight and thickness are made from metals having different densities. Which disc will have the larger rotational inertia about its central axis?

A. Disc with larger density

B. Disc with smaller density

C. Both discs will have same rotational inertia

D. None of the above

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4

A glass ball is shot to hit a wall from a point on a smooth floor. If the ball returns back to the point of projection in twice the time taken in reaching the wall, the coefficient of restitution between the glass ball and the wall is

A. 0.25

B. 0.33

C. 0.40

D. 0.50

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4

M.I. of a thin ring (external diameter D, internal diameter d) about an axis perpendicular to the plane of the ring, is

A. π/64 (D4 + d4)

B. π/32 (D4 - d4)

C. π/32 (D4 + d4)

D. π/32 (D4 × d4)

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4

Kinetic friction may be defined as

A. Friction force acting when the body is just about to move

B. Friction force acting when the body is in motion

C. Angle between normal reaction and resultant of normal reaction and limiting friction

D. Ratio of limiting friction and normal reaction

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4

The resultant of two forces P and Q acting at an angle θ, is

A. P2 + Q2 + 2P sin θ

B. P2 + Q2 + 2PQ cos θ

C. P2 + Q2 + 2PQ tan θ

D. √(P2 + Q2 + 2PQ cos θ)

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4

If two forces P and Q (P > Q) act on the same straight line but in opposite direction, their resultant, is

A. P + Q

B. P/Q

C. Q/P

D. P - Q

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4

A body of weight 14 g appears to weight 13 g when weighed by a spring balance in a moving lift. The acceleration of the lift at that moment was

A. 0.5 m/sec2

B. 0.7 m/sec2

C. 1 m/sec2

D. 1 cm/sec2

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4

The intrinsic equation of catenary is

A. S = c tan ψ

B. y = c cosh x/c

C. y = c cosh ψ

D. y = c sinh ψ

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4

The condition of equilibrium for any system of forces in a plane is

A. That polygon of forces must close

B. That resultant couple must be zero

C. Both (A) and (B)

D. None of the above

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4

Free body diagram is an

A. Isolated joint with only body forces acting on it

B. Isolated joint with internal forces acting on it

C. Isolated joint with all the forces, internal as well as external, acting on it

D. None of the above

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4

Two objects moving with uniform speeds are 5 m apart after 1 second when they move towards each other and are 1 m apart when they move in the same direction. The speeds of the objects are

A. 2 m/sec and 2 m/sec

B. 3 m/sec and 2 m/sec

C. 3 m/sec and 3 m/sec

D. 4 m/sec and 6 m/sec

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4

To attain the synchronous orbit, the launch of a satellite, is done from a place

A. On equator

B. On 30° latitude

C. On 45° latitude

D. On the poles

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4

A string of length 90 cm is fastened to two points A and B at the same level 60 cm apart. A ring weighing 120 g is slided on the string. A horizontal force P is applied to the ring such that it is in equilibrium vertically below B. The value of P is:

A. 40 g

B. 60 g

C. 80 g

D. 100 g

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4

Joule is the unit of

A. Power

B. Impulse

C. Work

D. Momentum

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4

A projectile is fired at an angle θ to the vertical. Its horizontal range will be maximum when θ is

A.

B. 30°

C. 45°

D. 90°

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4

Two forces act an angle of 120°. If the greater force is 50 kg and their resultant is perpendicular to the smaller force, the smaller force is

A. 20 kg

B. 25 kg

C. 30 kg

D. 35 kg

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4

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

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4

The unit of rotational inertia of a body in C.G.S system is

A. cm4

B. kg.cm²

C. gm.cm²

D. gm.cm3

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4

The force which produces an acceleration of 1 m/sec2 in a mass of one kg, is called

A. Dyne

B. Newton

C. Joule

D. Erg

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4

Which of the following represents the state of neutral equilibrium?

A. A cube resting on one edge

B. A smooth cylinder lying on a curved surface

C. A smooth cylinder lying on a convex surface

D. None of the above

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4

A particle is dropped from the top of a tower 60 m high and another is projected upwards from the foot of the tower to meet the first particle at a height of 15.9 m. The velocity of projection of the second particle is

A. 16 m/sec

B. 18 m/sec

C. 20 m/sec

D. 22 m/sec

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4

Three forces which act on a rigid body to keep it in equilibrium. The forces must be coplanar and

A. Concurrent

B. Parallel

C. Concurrent parallel

D. None of these

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4

A shell travelling with a horizontal velocity of 100 m/sec explodes and splits into two parts, one of mass 10 kg and the other of 15 kg. The 15 kg mass drops vertically downward with initial velocity of 100 m/sec and the 10 kg mass begins to travel at an angle to the horizontal of tan1 x, where x is

A. 3/4

B. 4/5

C. 5/3

D. 3/5

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4

Maximum efficiency of a screw jack for the angle of friction θ, is

A. sin θ/(1 + sin θ)

B. (1 - sin θ)/sin θ

C. (1 + sin θ)/(1 - sin θ)

D. (1 - sin θ)/(1 + sin θ)

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4

A ball which is thrown upwards, returns to the ground describing a parabolic path during its flight

A. Vertical component of velocity remains constant

B. Horizontal component of velocity remains constant

C. Speed of the ball remains constant

D. Kinetic energy of the ball remains constant

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4

The Law of Polygon of Forces states that

A. If a polygon representing the forces acting at point in a body is closed, the forces are in equilibrium

B. If forces acting on a point can be represented in magnitude and direction by the sides of a polygon taken in order, then the resultant of the forces will be represented in magnitude and direction by the closing side of the polygon

C. If forces acting on a point can be represented of a polygon taken in order, their sides of a polygon taken in order, their resultant will be represented in magnitude and direction by the closing side of the polygon, taken in opposite order

D. If forces acting on a point can be represented in magnitude and direction by the sides of a polygon in order, the forces are in equilibrium

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4

Cartesian form of the equation of catenary is

A. y = c cosh x/c

B. y = c sinh x/c

C. y = c tan x/c

D. y = c sin x/c

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4

The reaction at the support A of the beam shown in below figure is

A. 2 t

B. 5.8 t

C. 0.2 t

D. 3.5 t