MCQ
61. The unit of strain is- (BADC-18)
mm
N/mm
N-mm
no unit
None
ব্যাখ্যা: Strain is defined as "deformation of a solid due to
stress. Strain is a dimensionless unit since it is the
ratio of two lengths.
strain= change in length/original length
62. The term 'force' may be defined as an agent which produces or tends to produce, destroys or tends to destroy motion.
Agree
Disagree
63. The highest value of specific heat is found in- [PPA-19]
Alcohol
Kerosene
Methane
Water
ব্যাখ্যা: ব্যাখ্যা: Among all the four given liquids that is kerosene, methane, alcohol and water only water has the highest specific heat. The value of specific heat of water is 4.18 Joules per gram.
64. Deformation per unit length in the direction of force is known as- [PPA-19]
Strain
Lateral strain
Linear strain
Stress
ব্যাখ্যা: ব্যাখ্যা: Linear strain of a deformed body is defined as the ratio of the change in length of the body due to the deformation to its original length in the direction of the force.
65. The energy stored in a body when strained within elastic limit is known as- [MES-18]
resilience
strain energy
impact energy
proof resilience
66. The ultimate tensile stress for mild steel is - the ultimate compressive stress. [MES-18]
equal to
more than
less than
none of these
ব্যাখ্যা: ব্যাখ্যা: The ultimate tensile stress of mild steel is more than the ultimate compressive stress. Young modulus of a wire will be equal to stress for unit strain.
67. The unit of force in S.I. system of units is- [BB-20, BADC-18, MOD-20]
Dyne
Watt
Newton
Kilogram
ব্যাখ্যা: ব্যাখ্যা: Sl unit of force: Newton
SI-based unit of force: kg-m/sec^2
68. Young's modulus is the property of- [PPA-19]
Gas only
Solid only
Liquid and solid
Liquid only
ব্যাখ্যা: ব্যাখ্যা: Young's modulus is a mechanical property that measures the stiffness of a solid material.
69. The poisson's ratio for steel varies from- [BREB-17; MES-18]
0.22 to 0.27
0.32 to 0.42
0.25 to 0.33
0.31 to 0.34
ব্যাখ্যা: ব্যাখ্যা: Poisson's ratio values for different materiais.
Material Possion's ratio
Clay 0.30-0.45
Stainless steel 0.30-0.31
Steel (MS) 0.27-0.30
Castiron 0.21-0.26
70. The materials having same elastic properties in all directions are called- [PPA-19]
ideal materials
isotropic materials
elastic materials
uniform materials
ব্যাখ্যা: ব্যাখ্যা: Isotropic material means a material which have same or identical properties in all direction. Such as metal and glass.
71. If two forces of 3kg and 4kg act at right angles to each other, their resultant force will be- [MOCA-19]
7kg
14kg
5kg
7kg
ব্যাখ্যা: ব্যাখ্যাঃ
R=√P^2+Q^2+2PQCOSO
=√9+16+2x3 x4 x cox 90°
= √2
= 5kg
72. A material capable of absorbing large amount of energy before fracture is known as- উত্তর (PPA-19)
ductility
shock proof
toughness
resilience
ব্যাখ্যা: ব্যাখ্যা: The ability of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness.
73. The relation between Young's modulus (E) and Bulk modulus (K) is given by- [MES-18]
K=3m-2 /mE
K= mE/3(m-2)
K=3(m-2)/mE
K= mE / 3(m-2)
74. If a material expands freely due to heating it will develop- [PPA-19]
thermal stresses
no stresses
tensile stress
bending
ব্যাখ্যা: ব্যাখ্যা it, it will expand. Since it is unconstrained it expands freely and no stresses occur. That is the thermal strain is equal to the total strain. Thus, the mechanical strain is zero and thus the "thermal stress" is zero.
75. The unit of moment of inertia of an area is-[ IMES-18]
kg.m²
kg/m²
kg.m² s
m^4
ব্যাখ্যা: ব্যাখ্যা: Moment of intertia,
Ad^2= (mxm)x m^2= m^4
76. Two forces of 6 and 8kg act at right angles to each other, the resultant force will be- [PPA-19]
10
14
41
28
ব্যাখ্যা: ব্যাখ্যা: Given, F₁ =6kg. F₂=,8 kg. 0=90°
Resultant force,
R = √F₁^2+,F₂^2 + 2F₁F₂ cos0
√6^2+8^2+2x6x8 xcos90° = 10 kg.
77. If the resultant of two equal force has the same magnitude as either of the force, then the angle between the two forces is- [BADC-18]
30°
120°
60°
90°
ব্যাখ্যা: ব্যাখ্যা: Let the two forces be found F₂ at an angle x where
IF₁I =I F₂I = IRI
We know,
Resultant force,
R^2 = P² + Q^2+2PQcos0
F₁ ^2= F₁ ^2 + F₁ ^2+2 F₁ ^2cos0
F₁ ^2=2 F₁ ^2(1+cos0)
Cancelling F₁ ^2 on both sides
1=2(1+cos0)
Cos0 = 1/2
0=120°
78. The unit of power in S.I. unit is-[MES-18]
horsepower
kg.m
joule
watt
ব্যাখ্যা: The unit of power is watt. The unit of energy is joule.
79. Which of the following materials is most elastic? [PPA-19]
rubber
steel
plastic
brass
ব্যাখ্যা: ব্যাখ্যা: Both rubber and steel have elastic properties but steel is more elastie than rubber because steel comes back to its original shape faster than rubber when the deforming forces are removed. Steel has a higher elastic modulus (Young's modulus) than rubber.
80. The stress developed in the material without any permanent set is called. [MES-18]
elastic limit
breaking point
yield point
ultimate point
ব্যাখ্যা: ব্যাখ্যা: Elastic limit, maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation.