Fluids — Important Questions

The block will float because its density (0.9 g/cm³) is less than liquid density (1.2 g/cm³)

Step 1: Find density of block = mass/volume = 540 g / 600 cm³ = 0.9 g/cm³. Step 2: Compare with liquid density = 1.2 g/cm³. Since 0.9 < 1.2, the block is less dense than the liquid. Step 3: When density of object < density of liquid, the object floats. The buoyant force is greater than the weight of the block, pushing it upward. Step 4: Option B is wrong — it is the OBJECT's density vs liquid density that matters, not just which is denser. Option C (suspended) happens only when densities are exactly equal. Option D is incorrect — a floating body is never fully submerged.

The ship has a large hollow structure that increases its volume, making the average density of ship less than water

Step 1: The density of iron is about 7.8 g/cm³, which is much more than water (1 g/cm³). A solid iron nail sinks because its density > density of water. Step 2: A ship is not made of solid iron. It is hollow and contains a large volume of air inside it. Step 3: The average density = total mass / total volume (including air-filled hollow parts). This average density becomes less than water. Step 4: Because average density of ship < density of water, the buoyant force equals its weight and the ship floats — this is the law of flotation. Option B is scientifically wrong; the properties of iron do

Squeezing increases pressure, forcing water into the diver, increasing its average density above water

Step 1: When the bottle is squeezed, pressure inside the liquid increases (Pascal's law — pressure transmitted equally throughout). Step 2: This increased pressure compresses the air trapped inside the diver (pen cap), reducing the air volume. Step 3: Water enters the diver to fill the reduced air volume, increasing the mass of the diver without much change in its outer volume. Step 4: This increases the average density of the diver above that of water. Now weight > buoyant force, so the diver sinks. Step 5: Option B is wrong — squeezing does not reduce buoyant force by reducing water volume.

0.02 m³

Step 1: Buoyant force = True weight - Apparent weight = 600 - 440 = 160 N. Step 2: Buoyant force = weight of liquid displaced = V × ρ_liquid × g. Step 3: 160 = V × 800 × 10 = V × 8000. Step 4: V = 160 / 8000 = 0.02 m³. Step 5: This is the volume of the person (equal to volume of liquid displaced). Option B (0.055 m³) would result from using 600/10/1000 — incorrectly using weight of person. Option D uses wrong density or formula.