Mass and Weight Exercises with Solutions for 3rd Grade

Learn the difference between mass and weight with these 5 detailed exercises including definitions, rules, and step-by-step solutions.

Solution: Exercises 1 to 3
1 Understanding Mass vs Weight
Exercise 1
Sarah has a toy car that weighs 200 grams on Earth. What would its mass be on the Moon? What would its weight be?
Key Definitions:

Mass: The amount of matter in an object, measured in grams (g) or kilograms (kg). It stays the same everywhere.

Weight: The force of gravity acting on an object, measured in grams (g) or Newtons. It changes depending on gravity.

Method:
  1. Remember: Mass stays constant regardless of location
  2. Weight changes based on gravitational pull
  3. On the Moon, weight is about 1/6th of Earth's weight
Object
Toy Car
Earth Mass
200g
Moon Mass
200g
Step 1: Identify the mass

The mass of the toy car is 200 grams. This does NOT change.

Step 2: Calculate weight on Moon

Weight on Moon = Weight on Earth ÷ 6

Weight on Moon = 200g ÷ 6 ≈ 33g

Step 3: State final answers

Mass on Moon = 200g (same as Earth)

Weight on Moon ≈ 33g (much less than Earth)

Mass = 200g, Weight on Moon ≈ 33g
Final answer:

The toy car's mass remains 200g on the Moon, but its weight would be approximately 33g.

Applied rules:

• Mass Constant: Mass does not change with location

• Weight Variable: Weight depends on gravitational force

• Moon Gravity: About 1/6th of Earth's gravity

2 Comparing Masses
Exercise 2
Compare these items and order them from lightest to heaviest:
Apple: 150g
Book: 500g
Pencil: 5g
Water bottle: 250g
Definition:

Mass Comparison: Arranging objects by their mass measurements in ascending or descending order.

Items
Pencil: 5g, Apple: 150g, Water: 250g, Book: 500g
Order
Ascending
Result
5g < 150g < 250g < 500g
Step 1: List all masses

Pencil: 5g, Apple: 150g, Water bottle: 250g, Book: 500g

Step 2: Compare numbers

5 < 150 < 250 < 500

Step 3: Arrange from lightest to heaviest

Pencil (5g) → Apple (150g) → Water bottle (250g) → Book (500g)

Pencil < Apple < Water bottle < Book
Final answer:

From lightest to heaviest: Pencil (5g), Apple (150g), Water bottle (250g), Book (500g)

Applied rules:

• Numerical Comparison: Compare the numbers ignoring units

• Ascending Order: From smallest to largest number

• Unit Consistency: All measurements in same unit (grams)

3 Adding Masses
Exercise 3
Maria bought 3 apples. Each apple weighs 120g. What is the total mass of all apples?
Definition:

Total Mass: The sum of individual masses of multiple objects of the same type.

Number of Items
3 apples
Each Mass
120g
Total
360g
Step 1: Identify given information

Number of apples = 3, Mass of each apple = 120g

Step 2: Apply multiplication rule

Total mass = Number of items × Mass of each item

Total mass = 3 × 120g

Step 3: Calculate the result

3 × 120g = 360g

Step 4: State the final answer

The total mass of all apples is 360g

Total mass = 360g
Final answer:

The total mass of all 3 apples is 360 grams.

Applied rules:

• Multiplication Rule: Total mass = count × individual mass

• Unit Preservation: Answer has same unit as individual masses

• Consistency: All items must be the same type

Mass and Weight Fundamentals
Mass = Amount of Matter
Mass Definition
Mass
Constant Everywhere
Does not change location
Weight
Changes with Gravity
Varies by location
Units
Grams (g), Kilograms (kg)
Standard measurement
Key Concepts:

Mass: Amount of matter in an object (measured in g/kg)

Weight: Force due to gravity (affected by location)

Balance Scale: Compares masses by balancing forces

Measurement Techniques:
  1. Using Scales: Digital or balance scales for accurate measurement
  2. Estimation: Compare to known objects (e.g., apple ≈ 150g)
  3. Addition: Combine masses by adding measurements
  4. Comparison: Use greater than/less than symbols
Tip 1: Remember: Mass stays the same, weight changes with gravity!
Tip 2: Common reference weights: Paperclip = 1g, Apple = 150g, Textbook = 500g
Tip 3: Always include units (g or kg) in your answers
Tip 4: Check if all measurements use the same unit before comparing
Common Mistake: Confusing mass and weight - they are different concepts!
Memory Aid: "Mass" sounds like "matter" - it measures the amount of matter.
Essential Rules:

• Mass is always constant regardless of location

• Weight varies with gravitational pull

• 1 kilogram = 1000 grams

• Balance scales compare masses directly

Solution: Exercises 4 to 5
4 Converting Units
Exercise 4
Convert 2.5 kilograms to grams. Then convert 750 grams to kilograms.
Definition:

Unit Conversion: Changing from one unit of measurement to another while maintaining the same quantity.

Conversion
kg ↔ g
Factor
×1000
Result
2500g
Step 1: Know the conversion factor

1 kilogram = 1000 grams

Step 2: Convert kg to g (multiply)

2.5 kg = 2.5 × 1000 g = 2500 g

Step 3: Convert g to kg (divide)

750 g = 750 ÷ 1000 kg = 0.75 kg

Step 4: Verify conversions

Check: 0.75 kg = 750 g (reverse calculation)

2.5kg = 2500g, 750g = 0.75kg
Final answer:

2.5 kilograms equals 2500 grams, and 750 grams equals 0.75 kilograms.

Applied rules:

• Conversion Factor: 1 kg = 1000 g

• From kg to g: Multiply by 1000

• From g to kg: Divide by 1000

5 Balancing Scales
Exercise 5
On a balance scale, 3 oranges weigh the same as 2 apples. If each apple weighs 150g, what does each orange weigh?
Definition:

Balance Scale Principle: Both sides have equal mass when balanced.

Given
3 oranges = 2 apples
Apple Mass
150g each
Orange Mass
100g each
Step 1: Calculate total mass of apples

2 apples × 150g = 300g total

Step 2: Apply balance principle

3 oranges = 300g (same as apples)

Step 3: Find mass per orange

Mass per orange = Total mass ÷ Number of oranges

Mass per orange = 300g ÷ 3 = 100g

Step 4: Verify the answer

3 oranges × 100g = 300g, 2 apples × 150g = 300g ✓

Each orange weighs 100g
Final answer:

Each orange weighs 100 grams.

Applied rules:

• Balance Principle: Both sides equal when balanced

• Division Rule: Total mass ÷ number of items = mass per item

• Verification: Always check your answer

Mass and Weight Laws, Methods, Definitions
Mass = Matter Amount
Fundamental Concept
Key definitions:

Mass: Amount of matter in an object (constant, measured in g/kg)

Weight: Force of gravity on an object (variable, depends on location)

Gravity: Force that pulls objects toward planetary bodies

Complete methodology:
  1. Identify the concept: Determine if problem asks about mass or weight
  2. Check units: Ensure all measurements use the same unit
  3. Apply appropriate operation: Addition, subtraction, multiplication, or division
  4. Verify the result: Check if answer makes logical sense
Tip 1: Think of mass as "how much stuff" and weight as "how heavy".
Tip 2: A bathroom scale measures weight, not mass.
Tip 3: Balance scales compare masses directly.
Tip 4: Always write the unit (g or kg) with your answer.
Common errors: Mixing up mass and weight, forgetting units, incorrect conversions.
Key memorization: 1 kg = 1000 g, mass is constant, weight varies.
Essential rules to remember:

• Mass remains constant everywhere in the universe

• Weight changes depending on gravitational force

• 1 kilogram equals 1000 grams

• Balance scales work on the principle of equal masses

• Always include units in your final answer

Questions & Answers

Question: I'm confused about mass and weight. Are they the same thing? My mom says they're different but I don't understand how.

Answer: Great question! Mass and weight are related but different concepts:

  • Mass is how much "stuff" is in something - imagine counting every tiny piece that makes up an object. This never changes!
  • Weight is how heavy something feels because of gravity pulling on it.

Think of it this way: If you took your favorite toy to the Moon, it would still be made of the same amount of material (same mass), but it would feel much lighter because the Moon's gravity is weaker (different weight).

On Earth, we often use the same units (grams) for both, which can be confusing, but remember: mass is constant, weight changes with gravity!

Question: How can I estimate the mass of things around my house? I want to get better at knowing how much things weigh.

Answer: Estimating mass is a great skill! Here are some household reference points:

  • Small paperclip = 1 gram
  • Medium apple = 150 grams
  • Standard pencil = 5 grams
  • Full water bottle = 500 grams
  • Textbook = 500-800 grams

Practice by holding different objects and guessing their mass compared to these references. You can also use a kitchen scale to check your estimates!

Start with common items and gradually build your sense of how heavy different amounts feel.

Question: Why do we need to learn about mass and weight? When will I use this in real life?

Answer: Understanding mass and weight is very practical! Here are real-life applications:

  • Cooking and baking - recipes require specific amounts
  • Shopping - comparing package sizes and prices
  • Shipping packages - weight affects cost
  • Science experiments - measuring materials accurately
  • Health - understanding body weight changes

These skills also build mathematical thinking and help you understand the world around you. Even astronauts need to understand mass to navigate in space!

Learning to measure and compare is a fundamental life skill that connects to many other subjects too.