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Laws Of Motion Common Mistakes Class 11 Exam Prep Revision — Grandmaster Guide

A

Ayush (Founder)

Exam Strategist

Last Updated: 2026-06-01
  • F = ma
  • F = μN
  • F = (m₁ + m₂)v/(m₁ + m₂)
  • a = Δv/Δt
  • v = u + at
  • s = ut + (1/2)at²
  • v² = u² + 2as
  • F₁₂ = -F₂₁
  • T = 2π √(l/g)
  • W = F × s
  • P = Fv
  • K = (1/2)mv²
  • U = mgh
  • Impulse = Δp = FΔt

🪤 The 5 Mistakes That Cost Marks

  • Assuming friction is always kinetic, when ∈ fact it can be static or kinetic
  • Forgetting to consider the normal force ∈ problems involving inclined planes
  • Not using the correct equation for centripetal force: F = (mv²)/r
  • Incorrectly applying Newton's third law, forgetting that forces always come ∈ pairs
  • Not considering the system as a whole when applying conservation of momentum

✏️ 3 Solved PYQs

  • A block of mass 2 kg is moving with a velocity of 4 m/s on a frictionless surface. A force of 6 N is applied to the block ∈ the direction of motion. Calculate the acceleration of the block.
    • F = ma, so a = F/m = 6/2 = 3 m/s²
  • A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. Calculate the force applied by the brakes.
    • v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s²
    • F = ma, so F = 1500 × -1.67 = -2505 N
  • A particle of mass 1 kg is attached to a string of length 1 m. The particle is rotating ∈ a circular path with a velocity of 2 m/s. Calculate the tension ∈ the string.
    • F = (mv²)/r, so T = (1 × 2²)/1 = 4 N

🧠 The One Thing Most Students Get Wrong

  • Most students get the concept of pseudo force wrong. Pseudo force is a fictitious force that appears to act on an object when it is ∈ a non-inertial frame of reference. It is equal ∈ magnitude and opposite ∈ direction to the force that is actually acting on the object.

👁️ Ayush's Note

  • To solve problems ∈ laws of motion, always start by drawing a free body diagram. This will help you identify all the forces acting on the object and make it easier to apply Newton's laws.
  • Always consider the system as a whole when applying conservation of momentum.
  • Make sure to use the correct equation for centripetal force: F = (mv²)/r.
  • Pseudo force is a key concept ∈ laws of motion. Make sure you understand it well.

🔁 Last 5 Minutes Box

  • Last minute revision: go through all the formulas and make sure you understand the concepts of Newton's laws, friction, centripetal force, and pseudo force.
  • Check your notes and make sure you have all the formulas written down.
  • Go through the solved PYQs and make sure you understand the steps.
  • Take a few deep breaths and try to relax. You have prepared well for this exam.

📝 Practice MCQs

1. A block of mass 1 kg is moving with a velocity of 2 m/s on a frictionless surface. A force of 3 N is applied to the block ∈ the direction of motion. What is the acceleration of the block?

A) 1 m/s²

B) 2 m/s²

C) 3 m/s²

D) 4 m/s²

Answer: C) 3 m/s². Explanation: F = ma, so a = F/m = 3/1 = 3 m/s²

2. A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. What is the force applied by the brakes?

A) -1000 N

B) -1500 N

C) -2000 N

D) -2505 N

Answer: D) -2505 N. Explanation: v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s², F = ma, so F = 1500 × -1.67 = -2505 N

3. A particle of mass 1 kg is attached to a string of length 1 m. The particle is rotating ∈ a circular path with a velocity of 2 m/s. What is the tension ∈ the string?

A) 2 N

B) 3 N

C) 4 N

D) 5 N

Answer: C) 4 N. Explanation: F = (mv²)/r, so T = (1 × 2²)/1 = 4 N

4. A block of mass 2 kg is moving with a velocity of 4 m/s on a frictionless surface. A force of 6 N is applied to the block ∈ the direction of motion. What is the acceleration of the block?

A) 1 m/s²

B) 2 m/s²

C) 3 m/s²

D) 4 m/s²

Answer: B) 3 m/s². Explanation: F = ma, so a = F/m = 6/2 = 3 m/s²

5. A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. What is the distance traveled by the car before it comes to rest?

A) 50 m

B) 100 m

C) 150 m

D) 166.7 m

Answer: D) 166.7 m. Explanation: v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s², s = ut + (1/2)at² = 60 × (1000/3600) × 10 + (1/2) × -1.67 × 10² = 166.7 m


🚀 Ready to Ace Your Exam?

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This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.


📚 Related Topics

Continue your revision with these related guides:

  • 📖 World History Industrial Revolution Class 11 Exam Prep Revision — Grandmaster Guide
  • 📖 Motion In A Plane Class 11 Physics Revision — Grandmaster Guide
  • 📖 anatomy of flowering plants
  • 📖 physics heat light
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Prepared for Scholar
Date: 2026-06-01
CATEGORY: Exam Notes
  • F = ma
  • F = μN
  • F = (m₁ + m₂)v/(m₁ + m₂)
  • a = Δv/Δt
  • v = u + at
  • s = ut + (1/2)at²
  • v² = u² + 2as
  • F₁₂ = -F₂₁
  • T = 2π √(l/g)
  • W = F × s
  • P = Fv
  • K = (1/2)mv²
  • U = mgh
  • Impulse = Δp = FΔt

🪤 The 5 Mistakes That Cost Marks

  • Assuming friction is always kinetic, when ∈ fact it can be static or kinetic
  • Forgetting to consider the normal force ∈ problems involving inclined planes
  • Not using the correct equation for centripetal force: F = (mv²)/r
  • Incorrectly applying Newton's third law, forgetting that forces always come ∈ pairs
  • Not considering the system as a whole when applying conservation of momentum

✏️ 3 Solved PYQs

  • A block of mass 2 kg is moving with a velocity of 4 m/s on a frictionless surface. A force of 6 N is applied to the block ∈ the direction of motion. Calculate the acceleration of the block.
    • F = ma, so a = F/m = 6/2 = 3 m/s²
  • A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. Calculate the force applied by the brakes.
    • v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s²
    • F = ma, so F = 1500 × -1.67 = -2505 N
  • A particle of mass 1 kg is attached to a string of length 1 m. The particle is rotating ∈ a circular path with a velocity of 2 m/s. Calculate the tension ∈ the string.
    • F = (mv²)/r, so T = (1 × 2²)/1 = 4 N

🧠 The One Thing Most Students Get Wrong

  • Most students get the concept of pseudo force wrong. Pseudo force is a fictitious force that appears to act on an object when it is ∈ a non-inertial frame of reference. It is equal ∈ magnitude and opposite ∈ direction to the force that is actually acting on the object.

👁️ Ayush's Note

  • To solve problems ∈ laws of motion, always start by drawing a free body diagram. This will help you identify all the forces acting on the object and make it easier to apply Newton's laws.
  • Always consider the system as a whole when applying conservation of momentum.
  • Make sure to use the correct equation for centripetal force: F = (mv²)/r.
  • Pseudo force is a key concept ∈ laws of motion. Make sure you understand it well.

🔁 Last 5 Minutes Box

  • Last minute revision: go through all the formulas and make sure you understand the concepts of Newton's laws, friction, centripetal force, and pseudo force.
  • Check your notes and make sure you have all the formulas written down.
  • Go through the solved PYQs and make sure you understand the steps.
  • Take a few deep breaths and try to relax. You have prepared well for this exam.

📝 Practice MCQs

1. A block of mass 1 kg is moving with a velocity of 2 m/s on a frictionless surface. A force of 3 N is applied to the block ∈ the direction of motion. What is the acceleration of the block?

A) 1 m/s²

B) 2 m/s²

C) 3 m/s²

D) 4 m/s²

Answer: C) 3 m/s². Explanation: F = ma, so a = F/m = 3/1 = 3 m/s²

2. A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. What is the force applied by the brakes?

A) -1000 N

B) -1500 N

C) -2000 N

D) -2505 N

Answer: D) -2505 N. Explanation: v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s², F = ma, so F = 1500 × -1.67 = -2505 N

3. A particle of mass 1 kg is attached to a string of length 1 m. The particle is rotating ∈ a circular path with a velocity of 2 m/s. What is the tension ∈ the string?

A) 2 N

B) 3 N

C) 4 N

D) 5 N

Answer: C) 4 N. Explanation: F = (mv²)/r, so T = (1 × 2²)/1 = 4 N

4. A block of mass 2 kg is moving with a velocity of 4 m/s on a frictionless surface. A force of 6 N is applied to the block ∈ the direction of motion. What is the acceleration of the block?

A) 1 m/s²

B) 2 m/s²

C) 3 m/s²

D) 4 m/s²

Answer: B) 3 m/s². Explanation: F = ma, so a = F/m = 6/2 = 3 m/s²

5. A car of mass 1500 kg is moving with a velocity of 60 km/h. The driver applies the brakes and the car comes to rest ∈ 10 s. What is the distance traveled by the car before it comes to rest?

A) 50 m

B) 100 m

C) 150 m

D) 166.7 m

Answer: D) 166.7 m. Explanation: v = u + at, so a = (v - u)/t = (0 - 60 × (1000/3600))/10 = -1.67 m/s², s = ut + (1/2)at² = 60 × (1000/3600) × 10 + (1/2) × -1.67 × 10² = 166.7 m


🚀 Ready to Ace Your Exam?

Put your knowledge to the test! Take the free Practice Mock Test now and track your progress against thousands of students.

🎬 Watch video explanations on YouTube →


This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.


📚 Related Topics

Continue your revision with these related guides:

  • 📖 World History Industrial Revolution Class 11 Exam Prep Revision — Grandmaster Guide
  • 📖 Motion In A Plane Class 11 Physics Revision — Grandmaster Guide
  • 📖 anatomy of flowering plants
  • 📖 physics heat light