Questions on Resilience and Instantaneous Stress
Question.1. Define strain energy.
Answer.
The work done in straining the material, with in the elastic limit, is known as the strain energy. Mathematically,
Question.2. Define resilience.
Answer.
It is a common term used for the total strain energy stored in a body. Sometimes the resilience is also defined as the capacity of strained body for doing work (when it springs back) on the removal of the straining force.
Question.3. Define proof resilience.
Answer.
The maximum strain energy which can be stored in a body upto the elastic limit is called proof resilience. It is the mechanical property of material and it indicates their capacity to bear shock.
Question.4. Define modulus of resilience.
Answer.
The proof resilience per unit volume of a material is known as modulus of resilience.
Question.5. Define proof load.
Answer.
The maximum load which can be applied to a member without its being permanently deformed is called proof load.
Question.6. Name different modes of loading.
Answer.
(i) Gradually applied load,
(ii) Suddenly applied load,
(iii) Falling or impact load.
Question.7. State the difference between gradual loading and sudden loading.
Answer.
In gradual loading, the loading starts from zero and increases gradually till the body is fully loaded, while in sudden loading, the load is suddenly applied on the body.
Question.8. Derive an expression for the strain energy stored in a body when the load is gradually applied.
Answer.
Consider a bar of cross-sectional area 
and length 
subjected to an axial load W.
If 
be the extension in the bar and 
be the stress in the bar due to load W.
Hence
Question.9. Derive an expression for the instantaneous stress produced due to sudden load.
Answer.
Consider a tensile load 
be applied suddenly to a material which produces an extension 
. The work done will be given by 
. Suppose 
to be a load which increases gradually from zero and produces the same extension 
, then the work done is given by 
.
Since the bar is strained by an equal amount in each case, the strain energy is the same in each case, and consequently the applied energies will be equal.
Thus a suddenly applied load required to produce a given strain is just half the magnitude of that required, for the same strain, when gradually applied. Such a gradually applied load is called an equivalent load.
Multiple Choice Questions on Resilience and Instantaneous Stress
Question.1. The strain energy stored by a body with in elastic limit when loaded externally is called
(a) Resilience
(b) Proof resilience
(c) Modulus of resilience
(d) None of these
Question.2. Strain energy of a body may be defined as the work done on it
(a) To deform it
(b) To resist elongation
(c) To resist shortening
(d) All of these
Question.3. Strain energy is given by
(a) 
(b) 
(c) 
(d) None of these
Question.4. Modulus of resilience is equal to
(a) 
(b) 
(c) 
(d) 
Question.5. Strain energy stored in a body due to shear stress is given by
(a) 
(b) 
(c) Both of these
(d) None of these
Answers
1. (a) 2. (d) 3. (b) 4. (d) 5. (a)