scientific reasons[2 marks ]

Question 12 Marks

It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.

Answer

Blunt blades have larger area compared to the sharp-edged blades. Thus, the applied force produces a lower pressure in case of blunt blades, which makes it difficult to cut the cloth.

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Question 22 Marks

Two rods: A and B, having same weight and equal length have different thickness. Rod A is thinner while Rod B is thicker. They are held vertically on the surface of sand. Which one of them will sink more? Why?

Answer

Rod A will go deeper as it has a smaller area of contact, therefore the same force produces more pres¬sure. In case of rod B the same force produces less pressure.

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Question 32 Marks

An archer shoots an arrow in the air horizontally. However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain why the arrow ultimately falls down.

Answer

The initial force is muscular force which sets the arrow in motion. The force of gravity that acts on the arrow in the downward direction brings it to the ground.

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Question 42 Marks

Two persons are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied?

Answer

Both the persons are applying forces from opposite direction with equal magnitudes.

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Question 52 Marks

Why do sea divers wear specially designed suits?

Answer

Since the pressure of liquid increases with the increasing depth of sea. Specially designed suits protect scuba divers from the huge pressure of the water underneath.

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Question 62 Marks

We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why?

Answer

The pressure of air inside our body is same as that of the atmosphere. Therefore, we do not experience its effect.

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Question 72 Marks

Porters place a round piece of cloth on their head, when they have to carry heavy loads.

Answer

The round piece of cloth increases the area of contact of the load with the head, this reduces pressure and facilitates to carry the load.

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Question 82 Marks

Atmospheric pressure is so high as $10^5 N/m^2$, why are we not crushed by it ?

Answer

We are not crushed under this pressure, because pressure inside our bodies also equals the atmospheric pressure and cancels the pressure from outside.

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Question 92 Marks

The tools used for cutting and piercing always have sharp edges.

Answer

The cutting and piercing tools have very small area of cross$-$section which lead to increase in pressure with small force.
$-$So they can easily penetrate the surface.
$-$That’s why cutting tools are very much sharpened.

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Question 102 Marks

The shoulder bags are provided with broad straps.

Answer

We know that larger is the area of contact, the lesser is the pressure applied on an object.
$-$Shoulder bag with broad straps occupy larger area and do not exert too much pressure on the shoulders.
$-$Hence, we can easily carry the bag,

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Question 112 Marks

The nail is pushed into a wooden plank from its pointed end.

Answer

The area of the pointed end of nail is very small than that of its head.
$-$For the same force, large pressure can be created by small area of the surface.
$-$Therefore, the small force produce a pressure sufficient to push the pointed end of the nail into the wooden plank.

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Question 122 Marks

When we stop pedalling a bicycle, it gradually slow down and finally come to a stop.

Answer

When we stop pedalling a bicycle, the frictional force between tyres of bicycle and ground opposes the motion of a bicycle.
$-$Frictional force of air also opposes the motion of cycle.
$-$Therefore, bicycle speed gradually decreases and it comes to rest after travelling some distance.

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Science scientific reasons[2 marks ]

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