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Laws of Motion
Newton's laws, friction, circular motion dynamics
Key Concepts
- Newton's 1st law: an object continues its state unless acted on by a net force
- Newton's 2nd law: F = ma (net force causes acceleration)
- Newton's 3rd law: every action has an equal and opposite reaction
- Static friction ≤ μₛN; kinetic friction = μₖN (μₖ < μₛ)
- Pseudo force (−ma) must be added in non-inertial frames
Important Formulae
| Newton's 2nd law | F = ma |
| Static friction (max) | fₛ = μₛ N |
| Kinetic friction | fₖ = μₖ N |
| Angle of friction | tan θ = μ |
| Centripetal force | F = mv²/r = mω²r |
Quick Tips
- Normal force equals weight only on a horizontal surface with no vertical acceleration.
- Banking of roads: tan θ = v²/rg (ideal speed, no friction needed).
- Impulse = change in momentum = F × Δt.
Sample Practice Questions
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A bullet of 10 g is fired with 800 m/s from a gun of mass 5 kg. Recoil speed:
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Answer: 1.6 m/s
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Which law states that action and reaction are equal and opposite?
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Answer: Newton's third law
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A car takes a circular turn of radius 200 m at 72 km/h. For no skidding, minimum coefficient of friction (g=10):
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Answer: 0.2
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Angle of friction equals the angle whose tangent is:
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Answer: μs
Practice Questions
Practice 20 randomly selected NEET questions on Laws of Motion. Answers are revealed after each question.
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