A completely submerged 0.0004 m^3 cube is placed in water (ρ ≈ 1000 kg/m^3). What is the buoyant force acting on it? (g ≈ 9.8 m/s^2)

A completely submerged 0.0004 m^3 cube is placed in water (ρ ≈ 1000 kg/m^3). What is the buoyant force acting on it? (g ≈ 9.8 m/s^2)

• A. 3.92 N
• B. 9.8 N
• C. 0.392 N
• D. 19.6 N

Answer: (A)

Buoyant force equals the weight of the fluid that the object displaces. Since the cube is completely submerged, the displaced volume is the full cube volume, 0.0004 m^3. With water density about 1000 kg/m^3 and g ≈ 9.8 m/s^2, the buoyant force is F = ρ V g = 1000 × 0.0004 × 9.8 = 3.92 N. So the buoyant force is 3.92 newtons. If the object were not fully submerged, you’d use only the submerged volume in the same calculation.

Buoyant force equals the weight of the fluid that the object displaces. Since the cube is completely submerged, the displaced volume is the full cube volume, 0.0004 m^3. With water density about 1000 kg/m^3 and g ≈ 9.8 m/s^2, the buoyant force is F = ρ V g = 1000 × 0.0004 × 9.8 = 3.92 N. So the buoyant force is 3.92 newtons. If the object were not fully submerged, you’d use only the submerged volume in the same calculation.