Free Physics of Solids MCQs with Answers

131. A wire is stretched by a force that causes an extension. The energy is stored in it only when:

• A. The extension of wire is proportional to force applied
• B. The cross-section area of the wire remains constant
• C. The wire is not stretched beyond its elastic limit
• D. The weight of wire is negligible

Explanation: The energy stored in the wire is potential energy, when the wire is extended proportionally to the force applied PE=½ kx2. (c) is not a valid answer because the wire would still hold potential energy even when its stretched beyond its elastic limit.

132. Which of the following statements is correct:

• A. Elasticity is that property of body which enables body to regain its original dimension
• B. Elasticity is that property of a body that does not allow it to return to its original shape
• C. Elasticity is that property of a body that allows it to retain its original shape and dimension after the stress is removed
• D. Elasticity is that property of a body that obeys Hooke's law

Explanation: Elasticity is the ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed.

133. Three graphs for three types of materials are shown in the figure. Which row describes the correct materials?

• A. A
• B. B
• C. C
• D. D

Explanation: X is a ductile object; Y is a brittle object and Z is a polymer these graphs are a factual recall

134. Which feature of the following graph represents Young's Modulus?

• A. Area under graph
• B. Gradient of the graph
• C. Reciprocal of the gradient
• D. Product of gradient and area of the curve

Explanation: Young's modulus of elasticity (E), also known as the elastic modulus, is the ratio between stress and strain. Since the gradient of graph is strain/stress (gradient = x-axis/y-axis). So, its reciprocal would be equal to Young's modulus.

135. The stress-strain graph deduced the following limits successively:

• A. Proportional limit, yield limit, elastic limit
• B. Yield limit, elastic limit, proportional limit
• C. Proportional limit, elastic limit, yield limit
• D. Elastic limit, proportional limit, yield limit

Explanation: The following limits are deduced in the order; Proportional limit, elastic limit, yield limit.

136. A 4.0 m long wire is subjected to stretching force and its length increases by 40 cm. The percent elongation which the wire undergoes is:

• A. 0.10 %
• B. 40 %
• C. 10 %
• D. 20 %

Explanation: Given:Original length = 4mChange in length = 40 cm = 0.4 mPercentage elongation = ?Formula:To calculate the percentage elongation, we need to divide the change in length of the wire by its original length and then multiply by 100 to express it as a percentage. So,Percentage elongation = (Change in length / original length) × 100Percentage elongation = (0.4 / 4) × 100 = 0.1 × 100 = 10%

137. What is the strain energy per unit volume of a rod made from this metal when the strain of the rod is 0.010?

• A. 10 kJ m−3
• B. 100 kJ m−3
• C. 1.0 MJ m−3
• D. 10 MJ m−3

Explanation: To calculate the strain energy per unit volume (also known as strain energy density), you use the formula: strain energy per unit volume = (1/2) × stress × strain.Given that the strain is 0.010, and assuming the stress is calculated using Young's modulus of the material (for example, 2 × 109 Pa), the calculation would be:strain energy per unit volume = (1/2) × (2 × 109 Pa) × 0.010 = 10 × 106 J m−3 = 10 MJ m−3Thus, the correct answer is 10 MJ m−3. All other options are incorrect because they either underestimate or overestimate the strain energy density based on improper calculations or incorrect assumptions.

138. A diameter 'd' and length 'l' wire hangs vertically from a fixed point. The wire is extended by hanging a mass 'M' on its end. The Young modulus of the wire is 'E'. The acceleration of free fall is 'g'. Which equation is used to determine the extension 'x' of the wire?

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: Use the formula given:𝑥 =4𝑀𝑔𝑙 / 𝐸𝜋𝑑2

139. To determine Young's modulus of a material of a given wire of length 𝐿 we use:

• A. Melda's Apparatus
• B. Young's Apparatus
• C. Searle's Apparatus
• D. Cavendish Apparatus

Explanation: •Searle's apparatus is used for the measurement of Young's modulus. It consists of two equal-length wires that are attached to a rigid support.•Melde's Apparatus is a simple way to introduce students to the concept of standing waves. The apparatus consists of a string and an oscillator to generate different frequencies. Melde's experiment is ideal to study the behavior of standing waves. Supplied with accessories like pulley and clamp, scale pan, and cord.•Young's modulus apparatus is used to measure Young's modulus of a bar, not a wire.•By measuring the angle of the rod and knowing the twisting force (torque) of the wire for a given angle, Cavendish was able to determine the force between the pairs of masses, by using the Cavendish apparatus.

140. The Young's modulus of a given rod of uniform length 𝐿 is given by the relation:

• A. 𝐹𝐿/𝐴
• B. 𝐹𝐴/L
• C. F𝐿/𝜋𝑟2𝑙
• D. F𝑙/𝜋𝑟2L

Explanation: Young modulus=stress/strain FL/Al where l is the extension