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Science scientific reasons[2 marks ]

Friction · Bihar Board (BSEB) STD 8 (BSEB - English Medium). 10 questions.

Questions

scientific reasons[2 marks ]

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10 questions · self-marked practice — reveal the answer and mark yourself.

Question 12 Marks
Airplanes are designed to have streamlined shape.
Answer
$-$Force exerted by the fluid $($air$)$ on the object depends on the
$(i)$ speed of object with respect to fluid
$(ii)$ shape of the object and
$(iii)$ nature of the fluid.
$-$When Airplanes are flying they do not have to lose energy while overcoming the frictional force exerted by air.
$-$In order to reduce the friction, airplanes are given special shape called streamlined shape.
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Question 22 Marks
Drops of the oil are poured in the sewing machine after some use of it.
Answer
$-$After some use of sewing machine, their parts are getting wear and tear due to the friction.
$-$To reduce this depreciation and for easy operation of the machine oil is poured in it.
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Question 32 Marks
The tyres of the cars, trucks and bulldozers are treaded.
Answer
Treaded tyres of cars, trucks and bulldozers provide better grip with the ground, so that vehicles can move safely without slipping on the road and accident can be avoided.
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Question 42 Marks
The attaches and other pieces of luggage are fitted with rollers.
Answer
$-$Rolling reduces the friction than sliding. It is always easier to roll than to slide a body over another.
$-$Therefore, it is convenient to pull attaches and luggage fitted with rollers.
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Question 52 Marks
Gymnasts apply some coarse substance on their hands.
Answer
$-$Gymnasts apply some coarse substance on their hands to increase friction.
$-$It gives better grip with the support during the exercise so he does not slip.
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Question 62 Marks
Brake pads are used in the brake system of the bicycle and automobiles.
Answer
$-$When the bicycle is in motion, the brake pads do not touch the wheels.
$-$When brake lever is pressed, these pads arrest the motion of the rim due to friction. The wheel stops moving.
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Question 72 Marks
A bicycle and motor mechanics uses grease between the moving parts of these machines.
Answer
$-$When the bicycle is in motion, the brake pads do not touch the wheels.
$-$When brake lever is pressed, these pads arrest the motion of the rim due to friction. The wheel stops moving.
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Question 82 Marks
The talcum powder is sprinkled on the carom board before playing.
Answer
$-$The surface of the carom board becomes smooth when talcum powder is sprinkled on it.
$-$It reduces the friction between surface of carom board and striker $-$ cookeries.
$-$Hence, cookeries move easily with less efforts on the carom board.
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Question 92 Marks
The sole of our shoes get worn out after a period of time.
Answer
$-$The sole of the shoes worn out after a period of time due to continuous rubbing of soles with the ground.
$-$It damages the spike of the sole slowly and soles become slippery.
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Question 102 Marks
The handle of cricket bat is usually rough.
Answer
$-$The handle of a cricket bat is rough, that increases the friction between handle and hand.
$-$It provides better grip on the handle.
$-$Therefore, the handle of cricket bat is usually rough.
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