Archimedes’ Principle – Long Answer Questions (CBSE Class 10 Science – Physics)

Medium Level (Application & Explanation)

Answer:

Archimedes’ Principle says an object in a fluid feels an upward buoyant force equal to the weight of the fluid displaced.
This upthrust acts opposite to the object’s weight.
If buoyant force is greater than the weight, the object floats; if it is less, the object sinks.
A ship floats because its shape makes it displace enough water to balance its weight.
A balloon rises in air because it displaces air and gets an upthrust from the air.
Even a person floating in a swimming pool experiences this upward buoyant force.
Thus, the principle applies to all fluids (liquids and gases) in the same way.

Answer:

A cork and an iron nail of equal mass are placed on water.
The cork floats, while the nail sinks.
The cork has lower density and larger volume for the same mass.
It displaces more water, and that water’s weight equals the cork’s weight.
The buoyant force balances its weight, so it floats.
The iron nail is denser and small in volume, so it displaces less water.
The buoyant force is not enough to balance its weight, so it sinks.

Answer:

A solid block of steel would sink because it displaces little water compared to its weight.
A ship is hollow and has a large volume, including air spaces.
This shape makes it displace a large volume of water.
The weight of displaced water becomes equal to the ship’s weight at the waterline.
Then the buoyant force balances the weight, and the ship floats.
Designers adjust the shape and volume to ensure safe stability.
This is a direct use of Archimedes’ Principle in engineering.

Answer:

A hydrometer floats in a liquid and sinks more or less depending on the liquid’s density.
In a denser liquid, it displaces the needed weight with less depth, so it floats higher.
In a less dense liquid, it needs to sink deeper to displace the same weight.
A lactometer uses the same idea to check the purity of milk.
Pure milk has a different density than diluted milk, so the reading changes.
Both instruments rely on buoyant force = weight of displaced liquid.
The scale on the stem shows the density or related value.

Answer:

Measure the crown’s weight in air using a balance.
Immerse it in water and measure the apparent loss in weight (this is the buoyant force).
That loss equals the weight of water displaced by the crown.
From the displaced water, find the volume of the crown.
Use mass and volume to get density and compare with pure gold density.
If densities differ, the crown is not pure.
This is the famous “Eureka” application of Archimedes’ idea.

Answer:

Both have the same weight, but their densities and volumes differ.
The wood has lower density, so for the same weight it has larger volume.
It displaces more water and gets a larger buoyant force, so it floats.
The iron has higher density and smaller volume for the same weight.
It displaces less water, so the buoyant force is less than its weight, and it sinks.
The key idea is the link between volume, displaced water, and upthrust.
Thus, density, not just weight, decides floating or sinking.

Answer:

A submarine controls its overall density by adjusting ballast tanks.
To dive, it fills tanks with water, increases density, and reduces buoyant force compared to weight.
It then sinks when weight becomes greater than the buoyant force.
To rise, it blows air into the tanks, forcing water out, and decreases density.
Now it displaces enough water to make the buoyant force equal to or greater than its weight.
This careful control of displaced volume and upthrust is pure Archimedes.
Stability and safety depend on precise tank control.

Answer:

Answer:

Floating level depends on the density of the fluid and object’s density.
If the oil is less dense than water, the buoyant force for the same submerged volume is smaller.
To balance its weight, the object must sink deeper in oil to displace more volume.
So it will float with more of it submerged in oil than in water.
If the fluid were denser than water, it would float higher.
The rule is: higher fluid density means less depth of immersion.
This follows straight from Archimedes’ Principle.

Answer:

Use a lactometer or a simple hydrometer based on buoyancy.
Pour the milk in a tall cylinder and gently lower the instrument.
Note how deep it sinks and read the scale.
Pure milk has a typical range of density; diluted milk (with water) has lower density.
Lower density makes the instrument sink deeper, showing adulteration.
The reading is due to weight of displaced milk balancing the instrument’s weight.
Thus, density change detected by buoyant force reveals the purity.

Remember: Key words to link in your mind are buoyant force, displaced fluid, density, float, sink, volume, and weight.