Objective Type Questions On Class 11 Physics Chapter 9 Mechanical Properties of Solids

(1) A copper and a steel wire of the same diameter are connected end to end. A deforming force F is applied to this composite wire which causes a total elongation of 1 cm. The two wires will have

[A] the same stress

[B] different stress

[C] the same strain

[D] different strain

Answer: A, D

(2) For an ideal liquid

[A] the bulk modulus is infinite

[B] the bulk modulus is zero

[C] the shear modulus is infinite

[D] the shear modulus is zero

Answer: A, D

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(3) A wire is suspended from the ceiling and stretched under the action of a weight F suspended from its other end. The force exerted by the ceiling on it is equal and opposite to the weight.

[A] tensile stress at any cross-section A of the wire is F/A

[B] tensile stress at any cross-section is zero

[C] tensile stress at any cross-section A of the wire is 2F/A

[D] tension at any cross-section A of the wire is F

Answer: A, D

(4) The stress-strain graphs for the two materials are shown in the figure.

[A] material (ii) is more elastic than material (i) and hence material (ii) is more brittle

[B] material (i) and (ii) have the same elasticity and the same brittleness

[C] material (ii) is elastic over a larger region of strain as compared to (i)

[D] material (ii) is more brittle than material (i)

Answer: C, D

(5) Consider two cylindrical rods of identical dimensions, one of rubber and the other of steel. Both the rods are fixed rigidly at one end to the roof. A mass M is attached to each of the free ends at the centre of the rods.

[A] both the rods will elongate but there shall be no perceptible change in shape

[B] the steel rod will elongate and change shape but the rubber rod will only elongate

[C] the steel rod will elongate without any perceptible change in shape, but the rubber rod will elongate and the shape of the bottom edge will change to an ellipse

[D] the steel rod will elongate, without any perceptible change in shape, but the rubber rod will elongate with the shape of the bottom edge tapered to a tip at the centre

Answer: the steel rod will elongate, without any perceptible change in shape, but the rubber rod will elongate with the shape of the bottom edge tapered to a tip at the centre

(6) A spring is stretched by applying a load to its free end. The strain produced in the spring is

[A] volumetric

[B] shear

[C] longitudinal and shear

[D] longitudinal

Answer: longitudinal and shear

(7) The temperature of a wire is doubled. The Young’s modulus of elasticity

[A] will also double

[B] will become four times

[C] will remain same

[D] will decrease

Answer: will decrease

(8) The maximum load a wire can withstand without breaking when its length is reduced to half of its original length, will

[A] be doubled

[B] be half

[C] be four times

[D] remain same

Answer: remain same

(9) Modulus of rigidity of ideal liquid is

[A] infinity

[B] zero

[C] unity

[D] some finite small non-zero constant value

Answer: zero

(10) A copper and a steel wire of the same diameter are connected end to end. A deforming force F is applied to this composite wire which causes a total elongation of 1cm. The two wires will have

[A] the same stress.

[B] different stress.

[C] the same strain.

[D] different strain.

Answer: A, D

(11) 9A rod of length l and negligible mass is suspended at its two ends by two wires of steel (wire A) and aluminium (wire B) of equal lengths (Fig. in below). The cross-sectional areas of wires A and B are 1.0 mm² and 2.0 mm², respectively.
(Y_Al 70 * 10⁹ Nm^{– 2} and Y_steel 200 * 10⁹ Nm^-2

[A] Mass m should be suspended close to wire A to have equal stresses in both the wires.

[B] Mass m should be suspended close to B to have equal stresses in both the wires.

[C] Mass m should be suspended at the middle of the wires to have equal stresses in both the wires.

[D] Mass m should be suspended close to wire A to have equal strain in both wires.

Answer: B, D

(12) The stress-strain graphs for two materials are shown in Fig. below (assume same scale)

[A] Material (ii) is more elastic than material (i) and hence material (ii) is more brittle.

[B] Material (i) and (ii) have the same elasticity and the same brittleness.

[C] Material (ii) is elastic over a larger region of strain as compared to (i).

[D] Material (ii) is more brittle than material (i).

Answer: C, D

(13) A rectangular frame is to be suspended symmetrically by two strings of equal length on two supports (Fig. in below). It can be done in one of the following three ways;

The tension in the strings will be

[A] the same in all cases.

[B] least in (a).

[C] least in (b).

[D] least in (c).

Answer: least in (b).

(14) A mild steel wire of length 2L and cross-sectional area A is stretched, well within elastic limit, horizontally between two pillars (Fig. in below). A mass m is suspended from the mid point of the wire. Strain in the wire is

[A] x² / 2 L²

[B] x / L

[C] x² / L

[D] x2² / 2 L

Answer: x² / 2 L²

(15) A rigid bar of mass M is supported symmetrically by three wires each of length l . Those at each end are of copper and the middle one is of iron. The ratio of their diameters, if each is to have the same tension, is equal to

[A] (a)

[B] (b)

[C] (c)

[D] (d)

Answer: (b)

(16) The maximum load a wire can withstand without breaking, when its length is reduced to half of its original length, will

[A] be double.

[B] be half.

[C] be four times.

[D] remain same.

Answer: remain same.

(17) Modulus of rigidity of ideal liquids is

[A] infinity.

[B] zero.

[C] unity.

[D] some finite small non-zero constant value.

Answer: zero

(18) Streamline flow is more likely for liquids with

[A] low density and high viscosity

[B] low density and high viscosity

[C] high density and high viscosity

[D] high density and high viscosity

Answer: low density and high viscosity

(19) The Poisson’s ratio of a material is 0.5. If a force is applied to a wire of this material, there is a decrease in the cross-sectional area by 4%. The percentage increase in the length is

[A] 4%

[B] 2.5%

[C] 2%

[D] 1%

Answer: 4%

(20) In Bernoulli’s theorem which of the following is conserved?

[A] Energy

[B] Mass

[C] Linear momentum

[D] Angular momentum

Answer: Energy

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