Two mark Questions and Answers

TWO MARK QUESTIONS AND ANSWERS

1. Define stress.

When an external force acts on a body, it undergoes deformation and at the same time the body resists deformation. The magnitude of the resisting force is numerically equal to the applied force. This internal resisting force per unit area is called stress.

2. Define strain.

When a body is subjected to an external force, there is some change of dimension in the body. Numerically the strain is equal to the ratio of change in length to the original length of the body.

3. State Hooke's law.

It states that when a material is loaded, within its elastic limit, the stress is directly proportional to the strain.

4. Define factor of safety.

It is defined as the ratio of ultimate tensile stress to the permissible stress (working stress).

5. State tensile stress and tensile strain.

When a member is subjected to equal and opposite axial pulls, the length of the member is increased. The stress is induced at any cross section of the member is called Tensile Stress and the corresponding strain is known as Tensile Strain.

6. Define compressive stress and compressive strain.

When a member is subjected to equal and opposite pushes as shown in Fig., the length of the member is shortened. The stress produced at any cross section of the member is called compressive stress.

The ratio of decrease in length to the original length is known as compressive strain.

7. Define shear stress and shear strain.

The two equal and opposite forces act tangentially on any cross sectional plane of a body tending to slide one part of the body over the other part. The stress induced in that section is called shear stress and the corresponding strain is known as shear strain.

8. State volumetric strain.

Volumetric strain is defined as the ratio of change in volume to the original volume of the body.

9. Define modulus of elasticity.

When a body is stressed, within its elastic limit, the ratio of tensile stress to the corresponding tensile strain is constant. This ratio is known as Young's modulus.

10. Define Modulus of rigidity.

When a body is stressed, within its elastic limit, the ratio of shearing stress to the corresponding shearing strain is constant. This ratio is known as Modulus of rigidity.

11. State Bulk Modulus.

When a body is stressed, within its elastic limit, the ratio of direct stress to the corresponding volumetric strain is constant. This ratio is known as Bulk Modulus.

12. Define Poisson's ratio.

When a body is stressed within its elastic limit, the ratio of lateral strain to the longitudinal strain is constant for a given material.

13. State principal plane.

The planes which have no shear stress are known as principal planes. These planes carry only normal stresses.

14. Define principal stresses. 

The normal stresses acting on a principal plane are known as principal stresses. law, stress is proportional to strain.

15. According to ―― law, stress is proportional to strain.

Ans. Hooke's law.

16. The Poisson's ratio for a material cannot be more than ――.

Ans. 0.5

17. State the relationship between Young's modulus and Modulus of rigidity.

18. Give the relationship between Bulk modulus and Young's modulus.

19. The principal stress is ―― to the plane and the shear stress is ―― to the plane.

Ans. Normal, Tangential.

20. What do you understand by a compound bar?

A composite member is composed of two or more different materials which are joined together so that the system is elongated or compressed as a single unit.

21. What are the types of elastic constants?

There are three types of elastic constant.

They are,

1. Modulus of Elasticity or young's Modulus, E,

2. Bulk Modulus, K,

3. Shear Modulus or Modulus of Rigidity, G.

22. Write two equations used to find the forces in compound bars made of two materials subjected to tension.

23. What is stability?

The stability may be defined as an ability of a material to withstand high load without major deformation.

24. Define strain energy density.

Strain energy density is defined as the maximum strain energy that can be stored in a material within the elastic limit per unit volume. It is also known as modulus of resilience.

25. Determine the Poisson's ratio and bulk modulus of a material for which A Young's modulus is 1.2 × 105 N/mm2 and modulus of rigidity is 4.8 × 104 N/mm2.

Solution: 

We know that,

We know that,

26. Give the relation for change in length of a bar hanging freely under its own weight.

where P → Axial load.

L → Length of the bar.

E → Young's modulus of the bar.

A → Area of the bar

27. A brass rod 2 m long is fixed at both its ends. If the thermal stress is not to exceed 76.5 N/mm2, calculate the temperature through which the rod should be heated. Take the values of a and E as 17 × 10-6/K and 90 GPa respectively. 

Solution: 

We know that,

Thermal stress, σ = α Τ Ε

⇒ 76.5 = 17 × 10-6 × T × 90 × 103

[⸪ 90GPa = 90 × 109 = 90 × 109 N/m2 = 90 ×103 N/mm2]

Result: 

Temperature, T = 50 K