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A heavy plank of mass $100 kg$ hangs on three vertical wires of equal length arranged symmetrically (see figure). All the wires have the same cross-section. The middle wire is of steel and the other two are of copper. The modulus of elasticity of steel is assumed to be double that of copper. Determine the tensions in the wires. ( Use $g = 9.8 m s^{- 2}$ )

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Important Questions on Elasticity

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Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A uniformly tapering conical wire is made from a material of Young's modulus

Y

and has a normal, unextended length

L

. The radii, at the upper and lower ends of this conical wire, have values

R

and

3 R

, respectively. The upper end of the wire is fixed to a rigid support and a mass

M

is suspended from its lower end. The equilibrium extended length, of this wire, would equal:

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

The bulk modulus of a spherical object is

B

. If it is subjected to uniform pressure

p

, the fractional decrease in radius is

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A solid sphere of radius r made of a soft material of bulk modulus K is surrounded by a liquid in a cylindrical container. A massless piston of area

a

floats on the surface of the liquid, covering entire cross-section of cylindrical container. When a mass m is placed on the surface of the piston to compress the liquid, the fractional decrement in the radius of the sphere

(\frac{d r}{r})

, is:

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A load of mass

M kg

is suspended from a steel wire of length

2 m

and radius

1.0 mm

in Searle's apparatus experiment. The increase in length produced in the wire is

4.0 mm .

Now the load is fully immersed in a liquid of relative density

2 .

The relative density of the material of load is

8 .

The new value of increase in length of the steel wire is:

HARD

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

An external pressure

P

is applied on a cube at

0 ° C

so that it is equally compressed from all sides.

K

is the bulk modulus of the material of the cube and

α

is its coefficient of linear expansion. Suppose we want to bring the cube to its original size by heating. The temperature should be raised by:

HARD

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A thin

1 m

long rod has a radius of

5 mm

. A force of

50 {π×10}^{3} N

is applied at one end to determine its Young's modulus. Assume that the force is exactly known. If the least count in the measurement of all lengths is

0.01 mm

, which of the following statements is false?

EASY

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

In materials like aluminium and copper, the correct order of magnitude of various elastic modulii is :

EASY

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

For a perfectly rigid body,

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Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A metal rod of length

L

and cross-sectional area

A

is heated through

T ° C

. What is the force required to prevent the expansion of the rod lengthwise?

[Y

= Young's modulus of the material of rod,

α =

coefficient of linear expansion

]

EASY

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A rubber cord of density

d,

Young's modulus

Y

and length

L

is suspended vertically. If the cord extends by a length

0.5 L

under its own weight, then

L

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

Young's moduli of two wires

A

and

B

are in the ratio

7 : 4

. Wire

A

2 m

long and has radius

R .

Wire

B

1.5 m

long and has radius

2 m m .

If the two wires stretch by the same length for a given load, the value of

R

is close to:

HARD

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A steel wire of diameter

0.5 mm

and Young's modulus

2 \times 10^{11} N m^{- 2}

carries a load of mass

M

. The length of the wire with the load is

1.0 m

. A vernier scale with

10

divisions is attached to the end of this wire. Next to the steel wire is a reference wire to which a main scale, of least count

1.0 mm

, is attached. The 10 divisions of the vernier scale correspond to 9 divisions of the main scale. Initially, the zero of vernier scale coincides with the zero of main scale. If the load on the steel wire is increased by

1.2 kg

, the vernier scale division which coincides with a main scale division is __________. Take

g = 10 m s^{- 2} and π = 3.2

EASY

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

Copper of fixed volume

V

is drawn into wire of length

l

. When this wire is subjected to a constant force

F,

the extension produced in the wire is

∆ l .

Which of the following graph is a straight line?

HARD

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A bottle has an opening of radius

a

and length

b

. A cork of length

b

and radius

(a + ∆ a)

where

(∆ a ≪ a)

, is compressed to fit into the opening completely (see figure). If the bulk modulus of cork is

B

and the coefficient of friction between the bottle and cork is

μ

, then the force needed to push the cork into the bottle is

Question Image

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A wire is stretched such that its volume remains constant. The Poisson’s ratio of the material of the wire is:

EASY

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A metallic rod breaks when strain produced is

0.2 %

. Young's modulus of the material of the rod is

7 \times 10^{9} N m^{- 2}

. What should be its area of cross-section to support a load of

10^{4} N

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

Three thin wires of equal length are suspended from the top of a roof. The respective ratio of their area of cross section is

1 : 2 : 4

and Young's modulii is

4 : 2 : 1,

then the ratio of their weights to be attached at the other ends to obtain same elongation in them is

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A steel rail of length

5 m

and area of cross section

40 {cm}^{2}

is prevented from expanding along its length while the temperature rises by

10 ° C

. If coefficient of linear expansion and Young's modulus of steel are

1.2 \times 10^{- 5} K^{- 1}

and

2 \times 10^{11} N m^{- 2}

respectively, the force developed in the rail is approximately:

MEDIUM

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

The Young's modulus of steel is twice that of brass. Two wires of same length and of same area of cross-section, one of steel and another of brass are suspended from the same roof. If we want the lower ends of the wires to be at the same level, then the weights added to the steel and brass wires must be in the ratio of:

HARD

Physics>Mechanics>Elasticity>Hooke's Law and Modulus of Elasticity

A pendulum made of a uniform wire of cross sectional area A has time period T. When an additional mass M is added to its bob, the time period changes to

T_{M}

. If the Young's modulus of the material of the wire is

Y

, then

\frac{1}{Y}

is equal to:
(

g =

gravitational acceleration)

Important Questions on Elasticity

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