Kinetic Friction and Rough Inclines
For Coulomb sliding f_k=mu_k N; down a fixed incline a=g(sin theta-mu_k cos theta).
Why this shows up in the exam
Stopping distance · Rough inclines · Conveyor slip
Learn the idea
Sliding friction is mu_k N opposite relative surface velocity. On an incline, gravity drives along the plane while normal force sets friction.
🧠 Memory hook: Find N first; friction opposes slip.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- f_k = mu_k N — kinetic friction
- a = g(sin(theta)-mu_k cos(theta)) — down a rough incline
- v² = u²+2as — constant-acceleration follow-up
How to approach it
- 1Choose slip direction
- 2Find N
- 3Apply tangential dynamics then kinematics
Common slip-ups that cost marks
- •Taking N=mg on incline
- •Opposing acceleration
- •Using static friction while sliding
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A 2 kg block moves on a horizontal rough surface with coefficient of kinetic friction 0.2. A horizontal force of 10 N acts on it. Take g = 10 m/s^2. What is its acceleration?
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