AP Physics 1 Unit 3 Cheatsheet: Work, Energy, and Power

Translational Kinetic Energy

K = ½mv²

• Scalar quantity
• Frame-dependent (different observers measure different values)
• Depends only on mass and speed

Work Definition

Energy transferred into or out of a system by a force over a distance.

W = F∥d = Fd cos θ

• Only the force component parallel to displacement does work
• Scalar (can be positive, negative, or zero)
• Perpendicular force components change direction, not kinetic energy

The Core Relationship

ΔK = Σ W_i = Σ F∥,i d

Net work done on an object equals its change in kinetic energy.

Solving Strategy

• Identify all forces acting on the system
• Find the component of each force parallel to displacement
• Calculate work for each force: W = Fd cos θ
• Sum all work values
• Set equal to ΔK = K_f − K_i

Common Error

Forgetting that only parallel components contribute to kinetic energy change. A perpendicular force (like normal force on a horizontal surface) does zero work.