Engineering Mechanics

21. According to Lami's theorem

  1. three forces acting at a point will be in equilibrium
  2. three forces acting at a point can be represented by a triangle, each side being proportional to force
  3. 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
  4. if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two
  5. none of the above.

Correct answer: (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

22. According to law of triangle of forces

  1. three forces acting at a point will be in equilibrium
  2. three forces acting at a point can be represented by a triangle, each side being proportional to force
  3. 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
  4. if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two
  5. none of the above.

Correct answer: (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

23. According to principle of moments

  1. if a system of coplanar forces is in equilibrium, then their algebraic sum is zero
  2. if a system of coplanar forces is in equilibrium, then the algebraic sum of their moments about any point in their plane is zero
  3. the algebraic sum of the moments of any two forces about any point is equal to moment of theiwesultant about the same point
  4. positive and negative couples can be balanced
  5. none of the above.

Correct answer: (B)
if a system of coplanar forces is in equilibrium, then the algebraic sum of their moments about any point in their plane is zero

24. According to principle of transmissibility of forces, the effect of a force upon a body is

  1. maximum when it acts at the center of gravity of a body
  2. different at different points in its line of action
  3. the same at every point in its line of action
  4. minimum when it acts at the C.G. of the body
  5. none of the above.

Correct answer: (C)
the same at every point in its line of action

25. Angle of friction is the

  1. angle between normal reaction and the resultant of normal reaction and the limiting friction
  2. ratio of limiting friction and normal reaction
  3. the ratio of minimum friction force to the friction force acting when the body is just about to move
  4. the ratio of minimum friction force to friction force acting when the body is in motion
  5. ratio of static and dynamic friction.

Correct answer: (A)
angle between normal reaction and the resultant of normal reaction and the limiting friction

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

  1. one-fourth of the total height above base
  2. one-third of the total height above base
  3. one-half of the total height above base
  4. three-eighth of the total height above the base
  5. none of the above.

Correct answer: (A)
one-fourth of the total height above base

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

  1. one-fourth of the total height above base
  2. one-third of the total height above base
  3. one-half of the total height above base
  4. three-eighth of the total height above the base
  5. none of the above.

Correct answer: (B)
one-third of the total height above base

28. Center of percussion is

  1. the point of C.G.
  2. the point of metacentre
  3. the point of application of the resultant of all the forces tending to cause a body to rotate about a certain axis
  4. point of suspension
  5. the point in a body about which it can rotate horizontally and oscillate under the influence of gravity.

Correct answer: (C)
the point of application of the resultant of all the forces tending to cause a body to rotate about a certain axis

29. Coefficient of friction is the

  1. angle between normal reaction and the resultant of normal reaction and the limiting friction
  2. ratio of limiting friction and normal reaction
  3. the friction force acting when the body is just about to move
  4. the friction force acting when the body is in motion
  5. tangent of angle of repose.

Correct answer: (B)
ratio of limiting friction and normal reaction

30. Coulomb friction is the friction between

  1. bodies having relative motion
  2. two dry surfaces
  3. two lubricated surfaces
  4. solids and liquids
  5. electrically charged particles.

Correct answer: (A)
bodies having relative motion

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