⚡ MODULE 10 — QUICK REVISION
30-Minute Complete Revision
One day before the exam? This page covers everything. Formula dump + Flashcards + Key mistakes + Memory tricks. Do not skip anything.
START YOUR 30-MINUTE REVISION TIMER
00:00:00
📋 SECTION 1 — CHAPTER SUMMARY (5 min)
Laws of Motion — At a Glance
NEWTON'S 1ST LAW
Body continues in state of rest or uniform motion unless acted by NET external force. Defines inertia (= mass). Three types: rest, motion, direction.
Key: Inertia is NOT a force. First Law defines inertial frames.
NEWTON'S 2ND LAW
F = dp/dt = ma (for const mass). NET force = mass × acceleration. F and a always in same direction. Apply in each coordinate axis separately.
Key: F is NET force. Always draw FBD first. Valid only in inertial frames.
NEWTON'S 3RD LAW
For every action, equal and opposite REACTION. Acts on DIFFERENT bodies. Same nature. Simultaneous. They do NOT cancel.
Key: "Different bodies" — action and reaction pair cannot cancel.
FRICTION SUMMARY
- Static: fs ≤ μsN (adjustable) | Kinetic: fk = μkN (fixed)
- μk < μs (always) | Independent of area of contact
- Angle of repose θ: tanθ = μs
- On incline: N = mg cosθ, not mg
- Body slides when applied force > fs_max = μsN
MOMENTUM SUMMARY
- p = mv (vector, [MLT⁻¹])
- Impulse J = FΔt = Δp = Area under F-t graph
- Conservation: If F_net = 0, total p is conserved
- Recoil: m₁v₁ + m₂v₂ = 0 (if initial p = 0)
- KE = p²/(2m) [useful formula]
📐 SECTION 2 — FORMULA DUMP (5 min)
All Critical Formulas
Newton's 2nd Law
F = ma
Momentum Form
F = dp/dt
Momentum
p = mv
Impulse
J = FΔt = Δp
KE from momentum
KE = p²/2m
Static friction (max)
fs = μsN
Kinetic friction
fk = μkN
Normal on incline
N = mg cosθ
Accel on rough incline
a = g(sinθ - μcosθ)
Angle of repose
tanθ = μs
Atwood tension
T = 2m₁m₂g/(m₁+m₂)
Atwood acceleration
a = (m₂-m₁)g/(m₁+m₂)
Lift up (accel)
N = m(g+a)
Lift down (accel)
N = m(g-a)
Centripetal force
F = mv²/r = mω²r
Banking (ideal)
tanθ = v²/rg
Min speed at top
v_min = √(gr)
Min speed at bottom
v_min = √(5gr)
Tension at bottom
T = m(g + v²/r)
T_bot - T_top
T_b - T_t = 6mg
Rocket thrust
F = v_rel|dm/dt|
Pseudo force
F_ps = -ma₀
Conical pendulum ω
ω = √(g/Lcosθ)
Pendulum in accel. frame
tanθ = a/g
🃏 SECTION 3 — FLASHCARDS (10 min)
Click Cards to Flip & Reveal
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🧠 SECTION 4 — MEMORY TRICKS (5 min)
Remember Faster, Longer
Friction direction trick
"Friction OPPOSES relative motion (or tendency of relative motion)."
If body moves right → friction acts left.
If body TENDS to move right (but hasn't) → friction still acts left (static friction anticipates).
If body moves right → friction acts left.
If body TENDS to move right (but hasn't) → friction still acts left (static friction anticipates).
Incline angle memory trick
"mg sinθ slides (along), mg cosθ compresses (perpendicular)."
Sin → along slope (S for slide).
Cos → compresses surface (C for compress = normal force component).
Sin → along slope (S for slide).
Cos → compresses surface (C for compress = normal force component).
Lift apparent weight mnemonic
"Accelerating up = feeling heavy. Accelerating down = feeling light."
Up acceleration: N = m(g+a) → heavy.
Down acceleration: N = m(g-a) → light.
Free fall: N = 0 → weightless.
Up acceleration: N = m(g+a) → heavy.
Down acceleration: N = m(g-a) → light.
Free fall: N = 0 → weightless.
Conservation law trigger
"Is the system isolated? F_net = 0? → Conserve momentum."
Isolated system = no external force → p₁ + p₂ = constant.
Explosion starts at rest → total final momentum = 0.
Isolated system = no external force → p₁ + p₂ = constant.
Explosion starts at rest → total final momentum = 0.
Centripetal force reminder
"Centripetal is a ROLE, not a TYPE."
Like how "driver" is a role — can be played by a human, robot, or autopilot.
Centripetal role is played by: tension (string), friction (road), gravity (orbit), normal force (loop), etc.
Like how "driver" is a role — can be played by a human, robot, or autopilot.
Centripetal role is played by: tension (string), friction (road), gravity (orbit), normal force (loop), etc.
Newton's 3rd Law trigger
"Find the pair: Same type, opposite direction, different body."
Earth pulls book (gravity) ↔ Book pulls Earth (gravity).
Floor pushes person (normal) ↔ Person pushes floor (normal).
Gun pushes bullet ↔ Bullet pushes gun.
Earth pulls book (gravity) ↔ Book pulls Earth (gravity).
Floor pushes person (normal) ↔ Person pushes floor (normal).
Gun pushes bullet ↔ Bullet pushes gun.
Atwood machine shortcut
"Tension = Harmonic mean of weights / 2."
T = 2m₁m₂g/(m₁+m₂). When m₁ = m₂, T = m₁g = m₂g.
When m₂ >> m₁, a → g and T → 2m₁g.
T = 2m₁m₂g/(m₁+m₂). When m₁ = m₂, T = m₁g = m₂g.
When m₂ >> m₁, a → g and T → 2m₁g.
FBD checklist
Every FBD must include ALL of:
✓ Weight (mg downward)
✓ Normal force (⊥ to surface, away)
✓ Tension (along string, away from body)
✓ Friction (oppose motion/tendency)
✓ Applied forces (given direction)
✓ Weight (mg downward)
✓ Normal force (⊥ to surface, away)
✓ Tension (along string, away from body)
✓ Friction (oppose motion/tendency)
✓ Applied forces (given direction)
🚨 SECTION 5 — LAST-MINUTE ALERTS (5 min)
Don't Lose Easy Marks
❌ Top 8 Mistakes to Avoid Tomorrow
- "Inertia is a force" → WRONG. It's a property.
- "Action-reaction cancel each other" → WRONG. Different bodies.
- Drawing centripetal force as extra arrow in FBD → WRONG. It's net inward force.
- Using N = mg on inclined plane → WRONG. N = mg cosθ.
- Friction independent of area means area plays NO role → Remember this explicitly.
- μk > μs → IMPOSSIBLE. Kinetic is always LESS than static.
- Writing T = F in connected body → WRONG. Tension < Applied force.
- Forgetting to resolve forces in BOTH directions on incline.
✅ Guaranteed Marks — Do These Right
- Definition of inertia: "Resistance of a body to change in its state of motion or rest"
- Newton's 2nd Law: "The rate of change of momentum is proportional to the applied force and takes place in the direction of force."
- Newton's 3rd Law: "For every action, there is an equal and opposite reaction acting on DIFFERENT bodies."
- FBD: Draw it. Label it. Write equations from it.
- Units: Every answer needs units. N, m/s², kgm/s, etc.
- Sign convention: Declare positive direction. Stick to it.
🎯
You've Covered Everything.
3 Laws. FBD protocol. Friction. Momentum. Circular motion. PYQ patterns. Exam strategy. The complete system is in your hands.
"Physics is not about remembering formulas. It's about knowing WHEN and WHY each formula applies. You now know both."