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Assertion : If we apply force to a lump ...

Assertion : If we apply force to a lump of putty or mud, they have no gross tendency to regain their previous shape.
Reason : This type of substances are called plastic substances.

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The correct Answer is:
To solve the question, we need to analyze both the assertion and the reason provided. ### Step-by-Step Solution: 1. **Understanding the Assertion**: - The assertion states that when a force is applied to a lump of putty or mud, they do not tend to regain their original shape after the force is removed. - This indicates that these materials undergo a permanent deformation when subjected to stress. 2. **Analyzing the Reason**: - The reason given is that such substances are classified as plastic substances. - Plastic substances are defined as materials that, when deformed, do not return to their original shape after the removal of the applied force. 3. **Connecting Assertion and Reason**: - The assertion is a specific observation about the behavior of putty and mud, while the reason provides a general classification of such behavior as plasticity. - Since the assertion correctly describes the behavior of putty and mud, and the reason explains why this behavior occurs (i.e., they are plastic substances), both statements are true. 4. **Conclusion**: - Since both the assertion and the reason are true, and the reason correctly explains the assertion, we conclude that the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion. ### Final Answer: Both assertion and reason are true, and the reason is the correct explanation of the assertion.
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    Materials get deformed when force is applied. Some of them regain their status when the applied force is removed. They are termed as elastic. Those of which not regaining are called plastic. There may be delay in the regaining in some materials. They are said to have got elastic aftereffect, since they have gone beyond the elastic limit. Repeated application and removal of force leads to fatigueness in the material. Fatigued materials may break at any point time and so are avoided. The stress strain graph for two materials A and B is shown in the following figure: The strength of the material A and B is S_(A) and S_(B) , respectively, while the longevity of plastic behaviour is L_(A) and L_(B) . Then

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