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4

A workman was working on a rail track. A young boy at a distance holds his ear close to the railway track. The boy was able to hear the sound of each blow or the workman twice. It is because

A. speed of sound is greater in steel than in air

B. speed of sound is greater in air than in steel

C. part of sound waves is reflected between rail tracks

D. the boy's ears are at a different distance from the source

Correct Answer :

A. speed of sound is greater in steel than in air


Related Questions

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4

Powder clings to the skin because of

A. cohesion

B. adhesion

C. capillary action

D. absorption

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4

A man stands in a lift which accelerates upwards. The resultant reaction force on the floor of the lift is

A. greater than the weight of the man

B. less than the weight of the man

C. same as the weight of the man

D. zero

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4

Sound waves in air are

A. transverse

B. longitudinal

C. transverse and longitudinal

D. neither transverse nor longitudinal

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4

Rays from the headlight of a motor car are rendered parallel by suitably using

A. a convex mirror behind it

B. a concave lens behind it

C. a concave mirror in front of it

D. a concave mirror behind it

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4

When a charged rod is brought near a collection of small pith balls, the balls

A. will jump rapidly up and down for a short time

B. will remain unaffected

C. Both (a) and (b) above

D. It will produce electric shock

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4

Among the following the most suitable material for the core of an electro-magnet is

A. steel

B. wood

C. soft iron

D. copper

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4

The ozone layer absorbs

A. Cosmic rays

B. Infrared rays

C. All radiations of light

D. Ultra violet rays coming from the sun

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4

Nichrome is used in electric heaters and irons because

A. it resists oxidation when red hot

B. its melting point is high

C. it has got 60 times the resistance of copper

D. All the above

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4

The heating element often used in an electric iron is

A. copper

B. tungsten

C. mica

D. nichrome

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4

In a freezer ice cubes will be formed more quickly in trays made of

A. rubber

B. plastic

C. aluminium

D. wood

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4

The leader of the team who succeeded in constructing the first nuclear reactor (an atomic pile) in the world was

A. Albert Einstein

B. Enrico Fermi

C. HJ Bhabha

D. Sir Isaac Newton

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4

When a body is immersed in a fluid the force of buoyancy of the fluid on the body depends on

A. the immersed volume of the body

B. density of the liquid

C. acceleration due to the gravity at the place

D. All the above

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4

The inability of a body to change its state of rest or uniform motion along a straight line is called its

A. momentum

B. velocity

C. acceleration

D. inertia

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4

Drinks kept in a vacuum flask remain hot or cold as the case may be for a long time because

A. both walls are silvered on the vacuum side

B. there is vacuum between the double walls

C. the cork is a poor conductor of heat

D. of all the above

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4

A man weighing 50 kg floats on water in a lake. His apparent weight is

A. 50 kg

B. 45 kg

C. zero

D. 150 kg

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4

The escape velocity of a satellite projected from the surface of the earth is independent of

A. the mass of earth

B. the mass of the satellite

C. the radius of the earth

D. gravitation of the earth

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4

The velocity of sound in air increases with

A. the rise of temperature

B. rise of its frequency

C. decrease in humidity

D. fall of temperature

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4

A bucket of water is hung from a spring balance. A piece of iron is suspended in the water without touching the sides or touching the bottom of the bucket. The reading of the spring balance

A. will increase

B. will decrease

C. does not change

D. varies with the increase of depth of the immersion of the iron piece

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4

Which is the densest planet of the solar system?

A. Sun

B. Jupiter

C. Mercury

D. Earth

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4

Skating on ice is possible because

A. the surface of ice is smooth

B. ice is cold

C. the pressure on the ice due to skate melts the ice by lowering its melting point forming a thin film of water

D. the pressure on the ice due to skate raises its melting point

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4

The function of a moderator in a nuclear reactor is

A. to absorb unwanted neutrons

B. to slow down the fast neutrons to secure more effective hits on other nuclei

C. to decrease the number of fissile nuclei

D. to increase the number of fissile nuclei

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4

The instrument used to measure the strength of electric current at a point is

A. Ammeter

B. Altimeter

C. Adrinometer

D. Anemometer

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4

Electron-volt is a unit of

A. power

B. velocity

C. energy widely used in nuclear physics

D. number of electrons

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4

When we tighten the string of a sitar or tanpura its pitch

A. remains the same

B. increases

C. decreases

D. None of the above

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4

Primary colours are

A. colours of the rainbow

B. colours in the spectrum of white light

C. colours which cannot be produced by mixing other colours

D. colours found in nature

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The velocity of sound in air increases with

A. the rise of temperature

B. rise of its frequency

C. decrease in humidity

D. fall of temperature

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4

A lactometer la used to

A. find out the specific gravity of liquids

B. measure the volumes of liquids

C. test the purity of milk

D. determine the strength of acid in car batteries

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4

Electron-volt is a unit of

A. power

B. velocity

C. energy widely used in nuclear physics

D. number of electrons

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4

In the electrical circuit of a house the fuse acts as

A. a thermopile

B. a load

C. a step down device

D. a safety device

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4

If an object is placed between two parallel plane mirrors, the number of images formed will be

A. 1

B. infinite

C. 0

D. 4