Density & Floating — Drills · Grade 8 Science
Chapter: Properties of MatterWhat these drills covers
By the end of Density & Floating you should be able to:
- I can calculate density from mass and volume.
- I can use average density to predict whether an object floats in a fluid.
- I can argue from density evidence without claiming a unique identity from an overlapping value.
6 questions, numeric, multiple choice and written answer, each with a worked explanation.
Vocabulary used: density, displacement, average density, model, evidence, system boundary, assumption.
Problem 1
A 50 g sample has volume 25 cm³. Find density.
Answer and explanation
2 g/cm³
50 ÷ 25 = 2.
Problem 2
Water rises from 30 mL to 42 mL when a solid is submerged. Find its volume.
Answer and explanation
12 cm³
42 − 30 = 12 mL = 12 cm³.
Problem 3
A block has mass 48 g and volume 6 cm³. What is its density in g/cm³?
Answer and explanation
8 g/cm³
density = mass/volume = 48/6 = 8 g/cm³.
Problem 4
A liquid has density 0.8 g/cm³. What is the mass of 50 cm³ of it, in grams?
Answer and explanation
40 g
mass = density × volume = 0.8 × 50 = 40 g.
Problem 5
An object floats in water (1.0 g/cm³). Its density must be
- greater than 1.0
- less than 1.0
- exactly 1.0
- unrelated
Answer and explanation
less than 1.0
Objects less dense than the fluid float.
Problem 6
A solid block is cut in half. Explain what happens to its mass, volume and density.
Answer and explanation
Mass and volume both halve, but density is the ratio of the two, so it is unchanged. Density is a property of the material rather than of the amount present, which is why it can be used to identify a substance regardless of sample size.
Response criteria
- State a scientifically accurate conclusion.
- Show the data, mechanism, or calculation that supports it.
- Include units, conditions, or limits where relevant.