Finding density from apparent weight
An object weighs 50 N in air and 30 N when fully submerged in water (ρ = 1,000 kg/m³, g = 10 m/s²). What is the object's density?
Answer D: explanation for every choice
A
This divides the submerged weight by the true weight. An object denser than water can't have a density below water's.
B
This assumes a submerged object must have the same density as water.
C
This uses the apparent weight (30 N) as the buoyant force.
D
Correct. Buoyant force = 50 − 30 = 20 N, so V = 20/(1,000 × 10) = 0.002 m³. Mass = 5 kg, so ρ = 5/0.002 = 2,500 kg/m³.
TakeawayBuoyant force = weight in air − weight in water = ρwatergV.
Equations usedBuoyant force (Archimedes)Density and specific gravity
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