Laws of Motion

What you'll learn

A from-scratch guide to inertia, momentum, force and friction — Newton's three laws explained with everyday Indian examples, a fully solved numerical, and free-body diagrams, built for CBSE Class 11 and your JEE/NEET/CUET foundation.

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Laws of Motion — solved practice questions

8 Class 11 Physics questions with step-by-step solutions. Attempt each, then reveal the answer.

1. Q1easy

   Newton's first law of motion is also known as the law of:

   • AInertia
   • BAcceleration
   • CAction and reaction
   • DGravitation
   Show answer & solution

   Correct answer: (A) Inertia

   Newton's first law states that a body continues in its state of rest or uniform motion unless acted upon by an external force; this property is inertia, so it is called the law of inertia.

2. Q2easy

   A force acts on a 10 kg body producing an acceleration of 2 m/s^2. The magnitude of the force is:

   • A20 N
   • B5 N
   • C12 N
   • D8 N
   Show answer & solution

   Correct answer: (A) 20 N

   Using Newton's second law, F = ma = 10 × 2 = 20 N.

3. Q3easy

   The SI unit of force is the:

   • AJoule
   • BNewton
   • CWatt
   • DPascal
   Show answer & solution

   Correct answer: (B) Newton

   The SI unit of force is the newton (N), where 1 N = 1 kg·m·s^-2. Joule, watt and pascal are units of energy, power and pressure.

4. Q4medium

   According to Newton's third law, the action and reaction forces are equal and opposite but act on:

   • AThe same body
   • BTwo different bodies
   • CThe same point of one body
   • DNo body
   Show answer & solution

   Correct answer: (B) Two different bodies

   Action and reaction forces always act on two different bodies, which is why they do not cancel each other.

5. Q5easy

   A body of mass 2 kg moves with a velocity of 3 m/s. Its linear momentum is:

   • A5 kg·m/s
   • B6 kg·m/s
   • C1.5 kg·m/s
   • D9 kg·m/s
   Show answer & solution

   Correct answer: (B) 6 kg·m/s

   Linear momentum p = mv = 2 × 3 = 6 kg·m/s.

6. Q6medium

   A 5 kg block rests on a horizontal surface with coefficient of friction 0.2 (g = 10 m/s^2). The maximum force of friction is:

   • A25 N
   • B5 N
   • C10 N
   • D50 N
   Show answer & solution

   Correct answer: (C) 10 N

   Limiting friction f = μN = μmg = 0.2 × 5 × 10 = 10 N.

7. Q7medium

   A block slides down a smooth (frictionless) incline of 30° with g = 10 m/s^2. Its acceleration along the incline is:

   • A10 m/s^2
   • B8.66 m/s^2
   • C5 m/s^2
   • D2.5 m/s^2
   Show answer & solution

   Correct answer: (C) 5 m/s^2

   On a frictionless incline, a = g sinθ = 10 × sin30° = 10 × 0.5 = 5 m/s^2.

8. Q8easy

   The impulse of a force is equal to the change in:

   • AForce
   • BMomentum
   • CVelocity
   • DEnergy
   Show answer & solution

   Correct answer: (B) Momentum

   Impulse = force × time = change in momentum, which follows directly from Newton's second law.

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