JEE PHYSICS MCQ: MECHANICAL PROPERTIES OF SOLIDS

1 Medium

1 of 1

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The general form of potential energy curve for atoms or molecules can be represented by the following equation

U\left( R \right) = \frac{A}{{{R^n}}} - \frac{B}{{{R^m}}}

. Here, R is the interatomic or molecular distance, A and B are coefficients,

n

and

m

are the exponents. In the above equation

View answer and explanation

Correct option: B

Second term represents the attractive part of the potential

Option B (Second term represents the attractive part of the potential) is correct because the negative sign in front of the second term indicates an attractive potential, as the potential energy decreases with increasing distance.

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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.