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Q1. What is a perfectly plastic body?

Solution

A body that does not tend to regain its original configuration on the removal of the deforming force is called a perfectly plastic body.

Q2. What do you mean by the elastic limit?

Solution

When the deforming force is increased, a limit is reached beyond which if the applied force is removed, the solid does not come back to its original shape or size but remains deformed. This limit is called the elastic limit.

Q3. What do you mean by stress?  Is it scalar or vector?

Solution

The restoring force developed per unit area of a deformed body is called stress.  It is a vector physical quantity.

Q4. Which is more elastic, steel or rubber? why?

Solution

Steel is more elastic than rubber, because the inter-atomic bonding strength is more in steel than that in rubber.

Q5. (a)  Which is more elastic:  rubber or glass? Why? (b)  Identical springs of steel and copper are equally stretched.  On which spring, more work will have to be done?

Solution

(a)  Glass is more elastic than rubber because for a given applied force per unit area, the strain produced in glass is much smaller than the strain produced in rubber. (b)  Y for steel is more that of copper.  Therefore, in order to produce the same extension, a larger force will have to be applied on the steel spring than the copper spring.