Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : Steel is used in the construction of buildings and bridges.
Reason R : Steel is more elastic and its elastic limit is high.
In the light of above statements, choose the most appropriate answer from the options given below

Solution

Physics sir · 4 steps

In physics, more elastic means harder to deform, and that is exactly what a bridge needs from steel.

1. What elastic means. In physics, a material is more elastic if it resists deformation more strongly and springs back fully when the load is removed. A larger Young's modulus means more elastic. This is not the everyday sense of stretchy.
2. Check Reason R. Steel has a Young's modulus of about 2 × 10¹¹ Pa, far larger than rubber's. So it strains very little under a heavy load. Its elastic limit is also high, so it can carry a large stress and still return to its original shape. R is correct.
3. Link R to A. A building or bridge must carry heavy loads without sagging much and without bending permanently. Small strain comes from the high modulus, and no permanent set comes from the high elastic limit. So these two properties are the very reason steel is chosen. A is correct, and R explains it.
4. So. Both statements are true and R is the correct explanation of A, which is option (a).

The idea to keep. Physics elasticity is about the restoring tendency, not stretchiness: higher modulus means more elastic. For load-bearing structures, look for a high modulus and a high elastic limit.

Answer from the NTA final answer key. Solution by PrepWiser.