Kinetic energy & the work-energy principle
Practice Flashcards
Flip to reveal answersDefine kinetic energy.
Track your progress — Sign up free to save your progress and get smart review reminders based on spaced repetition.
All 11 Flashcards — Kinetic energy & the work-energy principle
Sign up free to track progress and get spaced-repetition review schedules.
Question
Define kinetic energy.
Answer
The energy an object has because it is **moving**. It depends on the mass and the **speed squared**. Unit: the joule (J).
Question
Formula for kinetic energy?
Answer
$E_k = \tfrac{1}{2}mv^{2} = \dfrac{p^{2}}{2m}$ — use ½mv² with the speed, or p²/2m with the momentum.
Question
You double an object's speed — what happens to its kinetic energy?
Answer
It becomes **four times** as big, because the speed is squared (2² = 4).
Question
State the work-energy principle.
Answer
The **net work done** on an object equals its **change in kinetic energy**: W_{net} = ΔE_k.
Question
How does friction stop a sliding object (in energy terms)?
Answer
Friction does **negative work**, removing kinetic energy. The object stops when all its E_k is used up.
Question
How do you find the distance a box slides to rest against friction?
Answer
Set **friction force × distance = E_k**, then **distance = E_k ÷ friction force**.
Question
What is the unit of kinetic energy?
Answer
The **joule (J)** — the same unit as work and all other forms of energy.
Question
When would you use E_k = p²/2m instead of ½mv²?
Answer
When you're **given the momentum** p (= mv) instead of the speed — both forms give the same energy.
Question
Find the E_k of a 3.0 kg object moving at 4.0 m s⁻¹.
Answer
E_k = ½ × 3.0 × 4.0² = ½ × 3.0 × 16 = 24 J.
Question
A 5.0 kg box has 90 J of E_k. Friction is 18 N. How far until it stops?
Answer
distance = E_k ÷ friction = 90 ÷ 18 = 5.0 m.
Question
Kinetic energy vs momentum — what's the key difference?
Answer
Kinetic energy ½mv² is a **scalar** (no direction) measured in joules; momentum mv is a **vector** measured in kg m s⁻¹.
Read the notes
Full study notes for Kinetic energy & the work-energy principle
Topic 1.3 hub
Work, energy and power
More from Topic 1.3
All flashcards in this topic
Physics exam skills
Paper structures & tips
Track your progress with spaced repetition
Sign up free — Aimnova tells you exactly which cards to review and when, so you remember everything before your IB exam.
Start Free