Work, Energy, and Power
Track how energy is transferred or transformed instead of memorizing isolated formulas.
Work, Energy, and Power
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Tell the energy story before selecting a formula
Work transfers energy when a force has a component along displacement. Kinetic energy belongs to motion, gravitational potential energy changes with height, and power measures how quickly energy is transferred.
Work–energy theorem
Net work equals the change in kinetic energy.
Power
Two machines may do equal work but have different power because their times differ.
Write the energy story first
Problem: A 2-kg ball moves at 4 m/s. Find its kinetic energy.
Recognize: Mass and speed are given, and speed must be squared.
Do it fast: KE=½(2)(4²)=16 J.
Why it works
Naming the initial and final energy forms reveals which quantities matter and reduces formula confusion.
Five forms you should recognize
A 30-N force moves a box 4 m in the same direction:
W=(30)(4)=120 JIf the force were perpendicular to the motion, its work would be zero.
For a 3-kg object at 4 m/s:
KE=½(3)(4²)=24 JDoubling speed makes kinetic energy four times as large.
On a frictionless descent, lost gravitational potential energy becomes kinetic energy. Compare initial and final energy rather than treating the formulas separately.
Two students climbing the same stairs do equal work if their masses are equal. The one who finishes sooner produces greater average power.
A motor producing 600 J of useful output from 800 J input has:
efficiency=600/800×100%=75%The rest is transferred to less useful forms, not destroyed.
Check before you commit
- Forgetting the square in kinetic energy
- Using time in the work formula
- Calling force measured in joules
- Assuming energy is destroyed by friction
- Confusing work and power
- Allowing efficiency above 100%
Do you need the lesson-or just practice?
One original question in each form recommends your next step. It does not yet verify mastery.
Work at the level you need.
Foundations
Build the core procedure with immediate explanations.
Core Practice
Use mixed forms with less scaffolding.
UPCAT-Style Transfer
Apply the competency in unfamiliar representations.
Ready to verify this competency?
A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.
Work, Energy, and Power FAQ
Can a person feel tired while doing zero mechanical work?
Yes. Biology uses energy internally even if the object has no displacement.
Where does energy go with friction?
It is largely transferred to thermal energy and sometimes sound.
Continue your science review.
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