The method and the results are on the density and pressure lab. Do the analysis yourself first, then check the answers below.
Quick answer: Density is mass per unit volume, ρ = m ÷ V. These answers go with the Physics 9-10 lab on density and pressure: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
The model answers use the sample data in the results table. Your own values will differ a little, but the ranking and the main conclusions should be the same. Show each equation, each substitution and the final value with its unit.
Level: Physics grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: GCSE P3, IGCSE 1.8
Volume = 44.0 − 40.0 = 4.0 cm³; ρ = 31.2 ÷ 4.0 = 7.8 g/cm³ = 7800 kg/m³, so the bolt is steel (iron).
Question 4 Float or sink
The wooden cube (0.60 g/cm³) floats. The oil (0.92 g/cm³) floats. The bolt (7.8 g/cm³) and the stone (2.9 g/cm³) sink, because their densities are greater than 1.00 g/cm³.
Question 5 Fraction under water
A floating object displaces water equal to its own weight, so the submerged fraction = ρ(object) ÷ ρ(water) = 0.60 ÷ 1.00 = 0.60 (60 %).
Question 6 Reading uncertainty
Each reading has an uncertainty of ±0.5 cm³, so the rise has ±1.0 cm³. Bolt: 1.0 ÷ 4.0 × 100 = 25 %. Stone: 1.0 ÷ 15.0 × 100 = 6.7 %. The stone density is more reliable because its volume is larger.
Question 7 Improve the lab
Any two: use a larger sample, or several bolts together, to get a bigger volume change; use a displacement can with a small measuring cylinder; remove air bubbles from the solid; read the meniscus at eye level; use a smaller-diameter cylinder; repeat and average. Reducing the percentage uncertainty in V is the key idea.
