Elasticity - Short Question Answer | Physics Grade 11 Solution

Short Question Solution

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Elasticity - Short Question Answer | Physics Grade 11 Solution

Elasticity - Short Question Answer

Short Question Answers

1. Why do spring balances show wrong readings after long use?
Ans: When a spring balance has been used for a long time, elastic fatigue is developed. So, the spring of such balances takes a longer time to recover its original position and it shows wrong readings.
 
2. Will the young’s modulus of elasticity change if the load hanging on it is doubled? Why?
Ans: The young's modulus of the elasticity of a body is given by
γ = (F/A)/(e/l) = Fl/Ae    where, F/A = stress, e/l= strain
When the load hanging on the material is doubled, the young's modulus of the elasticity remains constant because the increase in load is balanced by the extension produced. The young's modulus of elasticity of a material is constant quantity.  It depends on their nature of material, but not on what stress is applied to it. Therefore, young’s modulus of elasticity remains same although the load hanging on it is changed.
 
3. What is elastic limit and breaking stress?
Ans: Elastic limit is the maximum point of deforming force up to which a material shows its elastic behaviour above which it shows plastic behaviour.
The breaking stress is the stress applied to a material by which the material gets fractured. So if more stress is applied, material will break. This is breaking stress.
 
4. Explain the physical meaning of Poisson’s ratio.
Ans: Poisson’s ratio is defined as the ratio of the lateral strain to the longitudinal strain within the elastic limit. Thus, the lateral strain β is directly proportional to the longitudinal strain α, i.e.
β ∝ α 
or, β = σα 
Poisson's ratio, σ = β/α = lateral strain/longitudinal strain 
 
5. Why bridges are declared unsafe after long use?
Ans: If the bridge is used for a long time, due to alternate cycles of stress and strain the bridge gets fatigue. Because of this, the elastic property of the bridge changes, and hence the strain produced for given stress in the bridge will be very large and ultimately the bridge may collapse. Hence the bridge is declared unsafe after long use.
 
6. Compare the mechanical properties of a steel cable, made by twisting many thin wires together, with those of solid steel rod of the same diameter.
Ans: After a very large plastic deformation a metal rod will change into wires; which ultimately increase the resistance to the plastic deformation. Here, the number of thin twisted wire has more strength and ductility than a single steel rod.
 
7. Explain in terms of breaking stress why elephant has thicker legs as compared to human beings?
Ans: We know, Stress = Force/Area
Since the area is inversely proportional to the stress, more the area less will be the value of stress, so the effect of force will be less in the legs of an elephant in comparison to the legs of human beings and so the elephant can bear the higher value of the load. Therefore, the elephant has thicker legs in comparison to human beings.
 
8. How will you justify that stone is more rigid than iron?
Ans: We know that for a rigid body, change in dimensions will be negligible for a given stress. Stone shows negligible strain for a given that by iron. Therefore, the stone is more rigid than iron.
 
9. Why are rubbers used as vibration absorber?
Ans: The rubber can be compressed or stretched easily because of its coiled form molecules. The area of the elastic hysteresis loop of rubber is large. It takes a long time during compressing and stretching. Being so, it can store a large amount of elastic potential energy and finally convert into heat energy. Thus, a rubber sheet absorbs vibration kinetic energy and releases it slowly to heat energy. Hence, the rubber sheets are used as a vibration absorber.

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