Inertia Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Inertia.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

The intrinsic tendency of an object to resist any change in its state of motion, whether at rest or moving.

Heavy things are stubborn—hard to start moving, hard to stop.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Inertia is quantified by mass — the more mass an object has, the more it resists acceleration.

Common stuck point: Inertia is not a force — it is a property of matter that resists the effect of forces.

Worked Examples

Example 1

easy
A 2 \text{ kg} book and a 10 \text{ kg} box are both at rest on a frictionless table. The same force of 5 \text{ N} is applied to each. Which object is harder to accelerate, and what is each object's acceleration?

Solution

  1. 1
    Inertia is the resistance of an object to changes in its motion, and it is directly related to mass. The 10 \text{ kg} box has more inertia.
  2. 2
    Acceleration of the book: a_{\text{book}} = \frac{F}{m} = \frac{5}{2} = 2.5 \text{ m/s}^2
  3. 3
    Acceleration of the box: a_{\text{box}} = \frac{F}{m} = \frac{5}{10} = 0.5 \text{ m/s}^2

Answer

a_{\text{book}} = 2.5 \text{ m/s}^2, \quad a_{\text{box}} = 0.5 \text{ m/s}^2
Inertia is the tendency of an object to resist changes in its state of motion. More massive objects have greater inertia and require more force to achieve the same acceleration.

Example 2

medium
A passenger in a car is not wearing a seatbelt. The car, traveling at 15 \text{ m/s}, suddenly stops in 0.3 \text{ s}. What happens to the passenger (mass 70 \text{ kg}) and what force would be needed to decelerate them at the same rate?

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
A hockey puck (0.17 \text{ kg}) slides on frictionless ice at 25 \text{ m/s}. A bowling ball (6 \text{ kg}) rolls at 3 \text{ m/s}. Which object has more inertia, and which is harder to stop?

Example 2

hard
An empty shopping cart (15 \text{ kg}) and a full one (60 \text{ kg}) are both pushed from rest with 40 \text{ N} for 2 \text{ s}. What is the final speed of each? How does this illustrate inertia?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

mass