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Dec 7, 2025

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Density Practice Questions and Detailed Answers

Los

@los

Density is one of the most useful concepts in physics... Show more

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Density

Examples

1 A student pours out 1 litre of a liquid and finds its mass is 0.7 kg. Calculate the
density of the liquid.

Step 1: Wri

Basic Density Calculations

Density is simply how much mass is packed into a given volume - think of it as how "heavy" something feels for its size. The formula is straightforward: density = mass ÷ volume.

When tackling density problems, always start by writing down what you know and what you're looking for. Then convert your units carefully - you'll usually work with either grams and cm³ or kilograms and m³, but stick to one system throughout.

The key trick is remembering your conversions: 1 litre = 1000 ml = 1000 cm³, and 1 kg = 1000 g. Get these right, and the rest becomes much easier.

Quick Tip: Always check your units match before plugging numbers into the formula - mixed units are the biggest source of errors in density calculations!

Finding Mass from Density

Sometimes you'll need to find mass instead of density, which means rearranging the formula. Don't panic - it's just basic algebra! If density = mass ÷ volume, then mass = density × volume.

The process stays the same: write down what you know, calculate any missing values (like volume from dimensions), then substitute into your rearranged formula. Remember that volume of a rectangular block is length × width × height.

Always double-check your final answer makes sense. A small wooden block shouldn't weigh 20 kg, and a tennis ball shouldn't have the same density as lead!

Study Smart: Practice rearranging the density formula until it becomes automatic - you'll use this skill in chemistry and other physics topics too.

Real-World Applications

Density is brilliant for identifying materials - that's how the miner can tell real gold $19 g/cm³$ from fool's gold $5 g/cm³$ . Even if the sample isn't perfectly pure, densities that are much closer to the real thing usually indicate authenticity.

Different states of matter have different densities too. Molten iron $7.0 g/cm³$ is less dense than solid iron $8.0 g/cm³$ , which explains why it expands when heated and contracts when cooling.

Water displacement is a clever way to measure volume of irregular objects. When something displaces 300 cm³ of water, that's exactly the volume of the object - no complicated measuring required!

Real Life: This is exactly how archaeologists test whether ancient artifacts are made from the materials they claim to be!

Floating and Sinking

Objects float when their density is less than the liquid they're in - that's why ice $about 0.9 g/cm³$ floats on water $1.0 g/cm³$ . This principle helps you solve tricky problems about boats, fish tanks, and floating objects.

When calculating maximum loads, remember to add up all the masses involved. A 1 kg fish tank plus 15.54 kg of water equals 16.54 kg total - too heavy for a shelf that only holds 16 kg!

For objects that start floating but gradually fill with water, calculate how much extra mass they can take before their overall density reaches 1.0 g/cm³. Once they hit that magic number, down they go!

Physics Fact: This is why damaged ships eventually sink - as water fills the hull, the ship's average density increases until it exceeds that of seawater.

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Dec 7, 2025

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4 pages

Density Practice Questions and Detailed Answers

Los

@los

Density is one of the most useful concepts in physics - it helps explain why ice floats, how ships stay afloat, and even how miners identify real gold! Understanding density calculations will give you the tools to solve loads of... Show more

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Basic Density Calculations

Density is simply how much mass is packed into a given volume - think of it as how "heavy" something feels for its size. The formula is straightforward: density = mass ÷ volume.

The key trick is remembering your conversions: 1 litre = 1000 ml = 1000 cm³, and 1 kg = 1000 g. Get these right, and the rest becomes much easier.

Quick Tip: Always check your units match before plugging numbers into the formula - mixed units are the biggest source of errors in density calculations!

Sign up to see the contentIt's free!

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Join milions of students

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Finding Mass from Density

Sometimes you'll need to find mass instead of density, which means rearranging the formula. Don't panic - it's just basic algebra! If density = mass ÷ volume, then mass = density × volume.

Always double-check your final answer makes sense. A small wooden block shouldn't weigh 20 kg, and a tennis ball shouldn't have the same density as lead!

Study Smart: Practice rearranging the density formula until it becomes automatic - you'll use this skill in chemistry and other physics topics too.

Sign up to see the contentIt's free!

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Real-World Applications

Water displacement is a clever way to measure volume of irregular objects. When something displaces 300 cm³ of water, that's exactly the volume of the object - no complicated measuring required!

Real Life: This is exactly how archaeologists test whether ancient artifacts are made from the materials they claim to be!

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Floating and Sinking

When calculating maximum loads, remember to add up all the masses involved. A 1 kg fish tank plus 15.54 kg of water equals 16.54 kg total - too heavy for a shelf that only holds 16 kg!

Physics Fact: This is why damaged ships eventually sink - as water fills the hull, the ship's average density increases until it exceeds that of seawater.