Work-Energy Theorem
The net work done on a body equals its change in kinetic energy, Wnet = DKE = mv2/2 - μ2/2.
What is Work-Energy Theorem?
The net work done on a body equals its change in kinetic energy, Wnet = DKE = mv2/2 - μ2/2.
Key formula / rule: Wnet = DKE, valid for constant and variable forces.
Key points
- Derive the work-energy theorem from the second law.
- Apply the theorem to problems with friction.
Common exam trap
Including only the applied force and ignoring friction in Wnet.
Definitions
- Term
Work-Energy Theorem
- Meaning
The net work done on a body equals its change in kinetic energy, Wnet = DKE = mv2/2 - μ2/2.
- Term
Work-Energy Theorem — explanation
- Meaning
The theorem short-circuits problems in which the force varies or the path is awkward, because only the endpoints matter. It applies to the net work of all forces, including friction.
Learning objectives
Derive the work-energy theorem from the second law.
Apply the theorem to problems with friction.
Formulae
- Key point
Wnet = DKE, valid for constant and variable forces.
- Key point
Kinetic energy is a scalar and never negative.
- Key point
Friction contributes negative work and dissipates energy as heat.
Prerequisites
PHY-U1-WEP-T1-S1-C1
Common mistakes
Including only the applied force and ignoring friction in Wnet.
Using the theorem with the work of a single force to find the full DKE.
Keywords
Work-Energy
Theorem
Practice preview
A 1000 kg car traveling at 20 m/s applies brakes and comes to a stop in 50 m. What is the average braking force applied by the car?…
medium
Which of the following statements about the Work-Energy Theorem is INCORRECT?…
easy
A 2 kg object initially moving at 3 m/s accelerates to 5 m/s. What is the net work done on the object?…
easy