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MCQ
20421. 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: 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°
20422. Which of the following materials is most elastic? [PPA-19]
rubber
steel
plastic
brass
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.
20423. 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
ব্যাখ্যাঃ R=√P^2+Q^2+2PQCOSO =√9+16+2x3 x4 x cox 90° = √2 = 5kg
20424. 1MPa (Mega Pascal) = ?[BREB-20]
145 psi
131 psi
401 psi
100 psi
ব্যাখ্যা:। MPa =1x10^6 Pa 10^6 N/m² =10^6 kg/ 9.81 m 10 ×2.20 lb/ 9.81 x(39.37)^2 inch^2 =144.68 =145 ps [1 MPa = 100^6 Pa) [1 Pa = 1 N/m²] [1 kg = 9.81N] (1 kg = 2.20 lb) [1m=39.37 inch]
20425. Young's modulus is the property of- [PPA-19]
Gas only
Solid only
Liquid and solid
Liquid only
ব্যাখ্যা: Young's modulus is a mechanical property that measures the stiffness of a solid material.
20426. The stress developed in the material without any permanent set is called. [MES-18]
elastic limit
breaking point
yield point
ultimate point
ব্যাখ্যা: Elastic limit, maximum stress or force per unit area within a solid material that can arise before the onset of permanent deformation.
20427. The materials having same elastic properties in all directions are called- [PPA-19]
ideal materials
isotropic materials
elastic materials
uniform materials
ব্যাখ্যা: Isotropic material means a material which have same or identical properties in all direction. Such as metal and glass.
20428. A material capable of absorbing large amount of energy before fracture is known as- উত্তর (PPA-19)
ductility
shock proof
toughness
resilience
ব্যাখ্যা: The ability of a metal to deform plastically and to absorb energy in the process before fracture is termed toughness.
20429. Deformation per unit length in the direction of force is known as- [PPA-19]
Strain
Lateral strain
Linear strain
Stress
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.
20430. The unit of force in S.I. system of units is- [BB-20, BADC-18, MOD-20]
Dyne
Watt
Newton
Kilogram
ব্যাখ্যা: Sl unit of force: Newton SI-based unit of force: kg-m/sec^2
20431. The unit of force in SI system is- [BB-20]
Newton
Kilogram
Dyne
Watt
ব্যাখ্যা: As per the second law of motion proposed by Newton, force is defined as the product of mass and acceleration. In both the Sl system and in MKS system, the unit of mass is kilogram and the unit of acceleration is m/s. Therefore, the unit of force is kg m/s, which is what we refer to as Newton or N.
20432. 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: 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
20433. The unit of moment of inertia of an area is-[ IMES-18]
kg.m²
kg/m²
kg.m² s
m^4
ব্যাখ্যা: Moment of intertia, Ad^2= (mxm)x m^2= m^4
20434. The ultimate tensile stress for mild steel is - the ultimate compressive stress. [MES-18]
equal to
more than
less than
none of these
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.
20435. The resultant of two forces P & Q (Such that P > Q) acting along the same straight line but in opposite direction is given by- [MOD-20]
P+Q
P-Q
P/Q
Q/P
ব্যাখ্যা: When a system of force is acting on an object, the difference between the forces is called the Resultant force. Example-A 3N force to the left and 10N force the right given a resultant force of 7N of the right.
20436. 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: 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.
20437. The polar moment of inertia of a solid circular shaft of diameter (D) is- [MOD-20]
πd³/16
πd³ /32
πd4/64
πd4/32
20438. The highest value of specific heat is found in- [PPA-19]
Alcohol
Kerosene
Methane
Water
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.
20439. The hottest planet is- [BB-20]
Mercury
Saturn
Jupiter
Venus
ব্যাখ্যা: Venus is the hottest planet in the solar system. Mercury-800°F (430°C) during the day, 290°F (-180°C) at (471°C), Saturn-minus 218"F (-138°C). night, Jupiter-minus 162°F (-108°C), Venus-880°F
20440. If a material expands freely due to heating it will develop- [PPA-19]
thermal stresses
no stresses
tensile stress
bending
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.