JEE PHYSICS MCQ: MECHANICAL PROPERTIES OF SOLIDS

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Consider the two statements.

I. Mach number is the ratio of strain to stress.

II. Sound waves in air are longitudinal while light waves in air are transverse.

Choose the correct option among the following.

View answer and explanation

Correct option: B

Statement I is false while statement II is true

Option B (Statement I is false while statement II is true) is correct because Mach number is a speed ratio, not a stress/strain ratio, and sound waves are longitudinal while light waves are transverse.

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A wire is stretched under a force. If the wire suddenly snaps the temperature of the wire The increases in length is

l

of a wire of length

L

by the longitudinal stress. Then the stress is proportional to A steel wire of length

l

and cross sectional area

\mathrm{A}

is stretched by

1 \mathrm{~cm}

under a given load. When the same load is applied to another steel wire of double its length and half of its cross section area, the amount of stretching (extension) is Assertion: From the relation

Y=\frac{F l}{A \Delta l},

we can say that, if length of a wire is doubled, its Young's modulus of elasticity will also becomes two times.

Reason: Modulus of elasticity is a material property. A wire can be broken by applying a load of 200 N. The force required to break another wire of the same length and same material, but double in diameter, is Assertion(A): If radius of cylindrical wire is doubled, then this wire can bear four times stress.

Reason(R): By doubling the radius, area of cross-section will become four times.