31. According to law of triangle of forces

(a) three forces acting at a point will be in equilibrium

(b) three forces acting at a point can be represented by a triangle, each side being proportional to force

(c) if three forces acting upon a patticle are represented in magnitude and direction by the sides of a triangle, taken in order, they will be in equilibrium

(d) if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two

(e) none of the above.

Ans: c

33. If a rigid body is in equilibrium under the action of three forces, then

(a) these forces are equal

(b) the lines of action of these forces meet in a point

(c) the lines of action of these forces are parallel

(d) (b) and (c) above

(e) none of the above.

Ans: d

36. D’ Alembert’s principle is used for

(a) reducing the problem of kinetics to equivalent statics problem

(b) determining stresses in the truss

(c) stability of floating bodies

(d) designing safe structures

(e) solving kinematic problems.

Ans: a

37. A heavy ladder resting on floor and against a vertical wall may not be in equilibrium, if

(a) the floor is smooth, the wall is rough

(b) the floor is rough, the wall is smooth

(c) the floor and wall both are smooth surfaces

(d) the floor and wall both are rough sur-faces

(e) will be in equilibrium under all condi-tions.

Ans: c

38. According to Lami’s theorem

(a) three forces acting at a point will be in equilibrium

(b) three forces acting at a point can be represented by a triangle, each side being proportional to force

(c) if three forces acting upon a particle are represented in magnitude and

direction by the sides of a triangle, taken in order, they will be in equilibrium

(d) if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two

(e) none of the above.

Ans: d

39. Two coplanar couples having equal and op-posite moments

(a) balance each other

(b) produce a couple and an unbalanced force

(c) are equivalent

(d) produce a moment of couple

(e) can not balance each other.

Ans: e

40. A framed structure is perfect if it contains members equal to

(a) 2n-3

(b) n-l

(c) ‘2n-l

(d) n – 2

(e) 3n-2.

where n = number of joints in a frame

Ans: a

42. The product of either force of couple with the arm of the couple is called

(a) resultant couple

(b) moment of the forces

(c) resulting couple

(d) moment of the couple

(e) none of the above.

Ans: d

43. In detennining stresses in frames by methods of sections, the frame is divided into two parts by an imaginary section drawn in such a way as not to cut more than

(a) two members with unknown forces of the frame

(b) three members with unknown forces of the frame

(c) four members with unknown forces of the frame

(d) three members with known forces of the frame

(e) four members with two known forces.

Ans: b

44. The center of gravity of a uniform lamina lies at

(a) the center of heavy portion

(b) the bottom surface

(c) the mid point of its axis

(d) all of the above

(e) none of the above.

Ans: c

45. Center of gravity of a solid cone lies on the axis at the height

(a) one-fourth of the total height above base

(b) one-third of the total height above base

(c) one-half of the total height above base

(d) three-eighth of the total height above the base

(e) none of the above.

Ans: a

46. Center of percussion is

(a) the point of C.G.

(b) the point of metacentre

(c) the point of application of the resultant of all the forces tending to cause a body to rotate about a certain axis

(d) point of suspension

(e) the point in a body about which it can rotate horizontally and oscillate under the influence of gravity.

Ans: c

47. Center of gravity of a thin hollow cone lies on the axis at a height of

(a) one-fourth of the total height above base

(b) one-third of the total height above base

(c) one-half of the total height above base

(d) three-eighth of the total height above the base

(e) none of the above.

Ans: b

48. The units of moment of inertia of an area are

(a) kg m2

(b) m4

(c) kg/m2

(d) m3

(e) kg/m4.

Ans: b

49. The center of percussion of the homogeneous rod of length L suspended at the top will be

(a) L/2

(b) L/3

(c) 3L/4

(d) 2L/3

(e) 3L/8.

Ans: d

50. The center of gravity of a triangle lies at the point of

(a) concurrence of the medians

(b) intersection of its altitudes

(c) intersection of bisector of angles

(d) intersection of diagonals

(e) all of the above.

Ans: a