Buoyancy and Density Comparison

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📚 Part 1: Multiple Choice

1. What is density?

The mass of an object only

The mass per unit volume of a material

The volume of an object only

2. Buoyant force on an object submerged in a fluid acts:

Downwards, toward the centre of Earth

Upwards, opposing gravity

Sideways, away from the object

3. Which object will float in freshwater (density of water ≈ 1.0 g/cm³)?

Object A: density 0.8 g/cm³

Object B: density 1.2 g/cm³

Object C: density 1.0 g/cm³

Object D: density 2.5 g/cm³

4. Check all that apply: Which factors can change whether an object floats?

The object's volume

The object's mass

The fluid's density (e.g. salt water vs fresh water)

The colour of the object

✏️ Part 2: Short Answers & Calculations

5. Match each term (A–D) with the correct definition (1–4).

A. Density

B. Buoyancy

C. Displacement

D. Relative density

1. The upward force a fluid exerts on an object

2. The mass of a substance divided by its volume

3. The volume of fluid moved aside when an object is placed in it

4. A comparison of a substance's density to the density of water

6. Calculation: A wooden block has mass 300 g and volume 400 cm³. Calculate its density in g/cm³. Will it float in freshwater? Show working.

7. Calculation: A small boat has mass 2,000 kg and displaces 2.0 m³ of water. Will it float? (Use water density = 1,000 kg/m³.) Show working.

8. In one or two sentences, explain why two objects with the same mass might behave differently in water.

📋 Answer Sheet with Explanations

1. What is density?

Answer: The mass per unit volume of a material

Explanation: Density is calculated as mass divided by volume (D = m/V). It tells us how much matter is packed into a given space.

2. Buoyant force on an object submerged in a fluid acts:

Answer: Upwards, opposing gravity

Explanation: According to Archimedes' principle, the buoyant force always acts upward, pushing against the downward force of gravity.

3. Which object will float in freshwater?

Answer: Object A: density 0.8 g/cm³

Explanation: Objects with density less than water (1.0 g/cm³) will float. Only Object A has a lower density than water.

4. Which factors can change whether an object floats?

Answers: The object's volume, The object's mass, The fluid's density

Explanation: Volume and mass determine the object's density. The fluid's density affects the comparison.

Color has no effect on buoyancy - only density matters for floating behavior.

5. Matching:

A-2: Density = mass divided by volume

B-1: Buoyancy = upward force from fluid

C-3: Displacement = volume of fluid moved aside

D-4: Relative density = comparison to water's density

6. Wooden block calculation:

Density = mass ÷ volume = 300 g ÷ 400 cm³ = 0.75 g/cm³

Yes, it will float.

Explanation: Since 0.75 g/cm³ < 1.0 g/cm³ (water's density), the wooden block

is less dense than water and will float.

7. Boat calculation:

Mass of displaced water = 2.0 m³ × 1,000 kg/m³ = 2,000 kg

Yes, it will float.

Explanation: The boat's mass (2,000 kg) equals the mass of water it displaces

(2,000 kg), so the buoyant force equals the boat's weight - it will float.

8. Why might objects with same mass behave differently in water?

Sample Answer: Objects with the same mass can have different volumes, giving them

different densities. The object with larger volume (lower density) will float, while the

object with smaller volume (higher density) may sink.

Buoyancy and Density Comparison

Buoyancy and Density Comparison

📚 Part 1: Multiple Choice

✏️ Part 2: Short Answers & Calculations

📋 Answer Sheet with Explanations

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