I keep getting “Work” questions wrong in Work, Energy & Power. What's the trap?
forgetting the cosθ — a force perpendicular to the motion does zero work.
The usual trap: forgetting the cosθ — a force perpendicular to the motion does zero work. How to avoid it: carrying a bag horizontally does no work against gravity, because the force is vertical. Go back to the definition — energy transferred by a force: W = F·d·cosθ, where θ is the angle between force and displacement.
Key point
Work
Common mistake
forgetting the cosθ — a force perpendicular to the motion does zero work.
Memory tip
carrying a bag horizontally does no work against gravity, because the force is vertical.
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