FOCUSED REVIEW
Focused Review: Work, Energy, and Power
Reinforce the highest-leverage ideas and representative problem-solving tools for Work, Energy, and Power.
TIME
Approximately 15 minutes
BEST FOR
Targeted reinforcement
FINISH WITH
A readiness check
After this focused review, you’ll be able to explain physical meaning, track energy forms and transfers, and use qualitative reasoning.
Choose how you want to review
Unit Alignment
This public Unit Review is aligned to the approved Physics Sensei mechanics architecture and is independent of textbook chapter numbering.
ARCHITECTURE: Physics Sensei Independent Mechanics
UNIT: MEC-U06 — Work, Energy, and Power
RESOURCE: Unit Review
PROFILE: Foundational college physics
BEST USED
✓ Before homework on work or energy
✓ Before a quiz or exam
✓ When choosing between force-based and energy-based methods
Your Review Plan
Complete these six stages in order. Each stage builds on the previous one and prepares you for the final readiness check.
6 Stages • Approximately 15 minutes.
Warm-Up Check
Before you begin, reactivate the core ideas. Attempt each item before revealing the answer.
ACTIVITY 1
Energy Changes
Identify the energy change before choosing an equation.
A cart speeds up while a forward force acts along its motion. What happens to its kinetic energy?
Reveal Answers
Its kinetic energy increases.
Why it works: Positive net work transfers energy into kinetic energy.
ACTIVITY 2
Energy Forms
Name the important energy forms in the initial and final states.
A ball falls from rest. Which energy decreases and which energy increases?
Reveal Answers
Gravitational potential energy decreases while kinetic energy increases.
Why it works: Energy changes form while total energy remains conserved.
ACTIVITY 3
Work Sign
Use force direction relative to displacement.
A friction force points opposite an object’s displacement. Is the work by friction positive, negative, or zero?
Reveal Answers
Negative.
Why it works: A force opposite displacement does negative work on the object.
Ready to strengthen your understanding? Now reinforce the essential concepts that control this unit.
Core Concepts
Rebuild the key energy relationships and connect each equation to its physical meaning.
KEY CONCEPT 1
Work Transfers Energy
Work describes energy transferred by a force acting through a displacement. The sign of work indicates whether that force tends to increase or decrease kinetic energy.
W = Fd cos θ; Wnet = ΔK
Example: A force along the displacement does positive work; a force opposite the displacement does negative work.
KEY CONCEPT 2
Potential Energy Stores Interaction Energy
Gravitational and elastic potential energies describe energy associated with configurations of interacting systems. Only changes in potential energy matter physically.
Ug = mgy; Us = ½kx2
Example: Choose a convenient zero level for gravitational potential energy and compare states.
KEY CONCEPT 3
Energy Conservation Organizes the Problem
With conservative interactions, kinetic and potential energies can transform into one another. With friction or external work, include the transfer or transformation explicitly.
Ki + Ui = Kf + Uf
Example: Friction does not destroy energy; it commonly transforms mechanical energy into thermal/internal energy.
Ready to apply these ideas? Work through representative applications before the confidence check.
Guided Practice
Apply the energy model deliberately: define the system, identify the states, choose the equation, and check units and signs.
PRACTICE 1
Roller-Coaster Energy
Track energy from a higher point to a lower point.
A coaster starts from rest high on a frictionless track and moves downward. What happens to gravitational potential energy and kinetic energy?
Reveal Answers
Gravitational potential energy decreases while kinetic energy increases by the same amount.
Why it works: With negligible friction, the lost potential energy becomes kinetic energy.
PRACTICE 2
Spring Launch
Identify the energy transformation.
A compressed spring launches a cart on a level frictionless track. Which energy form decreases and which increases?
Reveal Answers
Elastic potential energy decreases while kinetic energy increases.
Why it works: Stored elastic energy is converted into motion.
PRACTICE 3
Power Comparison
Separate total work from rate.
Two students climb the same stairs and gain the same gravitational potential energy, but one takes half the time. Who has greater average power?
Reveal Answers
The faster student has twice the average power.
Why it works: Power is energy transferred per unit time.
Ready to check your understanding? Solve the short checks without looking back at the concept cards.
Confidence Check
Use these questions to confirm that you can select and apply the correct energy model independently.
QUICK CHECK 1
Choose the Energy Model
Decide whether mechanical energy alone is conserved.
A block slides down a rough ramp. Is K + U alone constant?
Reveal Answers
No. Mechanical energy decreases as energy is transformed into thermal/internal energy.
Why it works: Friction changes the mechanical-energy account even though total energy remains conserved.
QUICK CHECK 2
Interpret Zero Work
Reason from force direction.
A normal force is perpendicular to the displacement of a box sliding horizontally. What work does the normal force do?
Reveal Answers
Zero work.
Why it works: Only the component of force parallel to displacement contributes to work.
QUICK CHECK 3
Power Meaning
Distinguish energy from rate.
Can two machines do the same total work but have different powers?
Reveal Answers
Yes.
Why it works: They can transfer the same energy in different amounts of time.
How did it go? Use the revealed explanations to identify one specific relationship to revisit if needed.
Summary
Take one final look at the most important ideas from this review.
KEY TAKEAWAY 1
Ask What Energy Changes
Identify initial and final energy forms before writing equations.
KEY TAKEAWAY 2
Track Transfers, Not “Losses”
When mechanical energy decreases, identify where the energy went.
KEY TAKEAWAY 3
Power Is a Rate
Work and energy are measured in joules; power is measured in watts and describes how quickly energy is transferred.
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