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Question 1

Q46. Ice is packed in saw dust because__:

saw dust is a good conductor of heat.

saw dust is poor conductor of heat.

saw dust does not stick to the ice.

saw dust will not get melted easily.

Answer

Answer : saw dust is poor conductor of heat.

Ice needs to absorb heat energy to melt and become water (called latent heat of fusion). Since sawdust is a poor conductor of heat with air filled spaces it takes more time for the ice to absorb the required heat energy. This allows ice to remain in solid state for more time when packed in saw dust.
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Question 2

Q47. Sound is heard over longer distances on rainy days because__:

sound travels slowly in moist air

sound travels faster in moist air

moist air does not absorb sound

moist air absorbs sound

Answer

Answer : sound travels faster in moist air

The speed of sound in a medium is inversely proportional to the square root of its density. Higher is the humidity in the air, greater will be the velocity of sound. Therefore, the speed of sound in moist air is more than that in dry air. This is why the sirens of mills, whistle of trains and others are heard up to longer distances on a rainy day than on a dry day.
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Question 3

Q48. What type of force acts on a car moving around a curve?

Centrifugal force

Cohesive force

Centripetal force

Gravitational force

Answer

Answer : Centripetal force

Any object moving in a circle (or along a circular path) experiences a centripetal force that pushes or pulls the object towards the center of the circle. In the case of a car moving along a curve, as it makes a turn, the force of friction acting upon the turned wheels of the car provides centripetal force required for circular motion. The net force on a car travelling around a curve is the centripetal force, F MV r c .. 2 , directed toward the center of the curve. To minimize the effect of this force, banking of curve is observed on curved paths.
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Question 4

Q49. What is the distance between a crest and a consecutive trough in a transverse wave ?

Amplitude

Wavelength

Half of the wavelength

Twice of wavelength

Answer

Answer : Half of the wavelength

Wavelength is defined as distance between two consecutive crest or troughs. Between two crests, there is a trough exactly in the middle of the two crests. Distance between crest and adjacent trough will be half of the distance between two crests or simply, half of the wavelength.
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Question 5

Q50. The amount of heat that is produced in a wire when electric current passes through does not depends on__:

Material

Length

Thickness

None of these

Answer

Answer : None of these

The amount of heat produced in a wire depends on its length, thickness, nature of the material, amount of current flowing and time for which the current flows. As such for different requirements, wires of different materials are used.
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