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JEE Main Laws of Motion — practice questions

Explore 67 free Laws of Motion questions in JEE Main Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Laws of Motion: quick revision

Choose the body or system, draw its free-body diagram and add the external forces. Apply Newton’s second law along convenient axes. Action and reaction forces act on different bodies, so they do not cancel in one body’s force equation.

Key ideas and when to use them

  • $\sum\vec F=m\vec a$ for constant mass in an inertial frame.
  • Kinetic friction: $f_k=\mu_kN$.
  • Static friction adjusts up to $f_s\leq\mu_sN$; it is not always at its maximum.

Common mistakes

  • The normal force equals mg only when the force balance supports that result.
  • Include the direction of friction and the net force, not just their magnitudes.

Three worked examples

Example 1: A 3 kg body experiences a net force of 18 N. Find its acceleration.
  1. Use the net external force.
  2. $a=18/3$.

6 m/s²

Example 2: A 2 kg object rests on a scale in a lift accelerating upward at 2 m/s². Use g = 10 m/s². Find the normal force.
  1. Upward force balance gives $N-mg=ma$.
  2. $N=2(10+2)$.

24 N

Example 3: A sliding block has normal force 40 N and kinetic-friction coefficient 0.25. Find the friction magnitude.
  1. The block is sliding, so use kinetic friction.
  2. $f_k=0.25\times40$.

10 N

Qallery AI-assisted study notes and original examples. Further reading: NCERT Physics — Laws of Motion.

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Laws of Motion questions and exercises with answers

Showing questions 1–30 of 67.

Newton's first law of motion is also known as the law ofRead the answer and worked solution →A cricket ball of mass 150 g moving at (3i+4j) m/s is hit to -(3i+4j) m/s. The magnitude of momentum change isRead the answer and worked solution →Conservation of linear momentum in a collision follows directly fromRead the answer and worked solution →A force F acts on a 2 kg body for 3 s, changing its speed from 2 m/s to 8 m/s along the line of F. The magnitude of F isRead the answer and worked solution →The maximum static friction force on a body is f = μN. Static friction is best described asRead the answer and worked solution →A 10 kg block on a frictionless surface is pulled by 20 N horizontally and 20 N at 60° above horizontal. The horizontal acceleration isRead the answer and worked solution →Impulse equalsRead the answer and worked solution →A body in equilibrium under several forces hasRead the answer and worked solution →A 0.5 kg ball hits a wall at 10 m/s and rebounds at 10 m/s. The impulse on the ball isRead the answer and worked solution →Newton's second law in vector form isRead the answer and worked solution →A lift accelerates upward at 2 m/s². The apparent weight of a 50 kg person (g=10) isRead the answer and worked solution →Two blocks of 2 kg and 3 kg connected by a string are pulled by 10 N on the 3 kg block (frictionless). The acceleration isRead the answer and worked solution →The SI unit of force, the newton, equalsRead the answer and worked solution →As per your syllabus, Aristotle's fallacy held that a force is required for which condition?Read the answer and worked solution →As per your syllabus, a ball released on a frictionless incline rises on the other side to which height?Read the answer and worked solution →As per your syllabus, INERTIA of a body is best described as which property?Read the answer and worked solution →As per your syllabus, Newton's FIRST law states which of the following?Read the answer and worked solution →As per your syllabus, the QUANTITATIVE measure of inertia of a body is which physical quantity?Read the answer and worked solution →As per your syllabus, the momentum p of a body of mass m moving with velocity v is which?Read the answer and worked solution →As per your syllabus, momentum p is a vector with direction along which vector?Read the answer and worked solution →As per your syllabus, why is a SHORTER stopping time more painful when catching a cricket ball?Read the answer and worked solution →As per your syllabus, when a stationary bus suddenly starts, passengers are jerked backward primarily because of which property?Read the answer and worked solution →As per your syllabus, a body moving on it must do which?Read the answer and worked solution →As per your syllabus, the SI unit of momentum is which?Read the answer and worked solution →As per your syllabus, Newton's SECOND law in SI units states which relation?Read the answer and worked solution →As per your syllabus, the SI unit of force is the newton, with one newton equal to which value?Read the answer and worked solution →As per your syllabus, the IMPULSE J of a force F acting for time Δt equals which quantity?Read the answer and worked solution →As per your syllabus, an IMPULSIVE FORCE is best described by which feature?Read the answer and worked solution →As per your syllabus, a 0.15 kg cricket ball at 12 m/s is hit back at 12 m/s along the same line. The impulse imparted is which value?Read the answer and worked solution →As per your syllabus, the dimensions of FORCE are which set?Read the answer and worked solution →

Worked practice questions

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

  1. acceleration
  2. action-reaction
  3. inertia
  4. gravitation
Show answer and solution

Correct answer: C. inertia

The first law (a body stays at rest or in uniform motion unless acted on by a net force) defines inertia.

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A cricket ball of mass 150 g moving at (3i+4j) m/s is hit to -(3i+4j) m/s. The magnitude of momentum change is

  1. 0
  2. 3.0 kg·m/s
  3. 1.5 kg·m/s
  4. 0.75 kg·m/s
Show answer and solution

Correct answer: C. 1.5 kg·m/s

We have Δp = m(v−u). That is Δp = 0.15·(−2)(3i+4j). So Δp = −0.3(3i+4j). |Δp| = 0.3·√(9+16) = 0.3·5 = 1.5 kg·m/s.

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Conservation of linear momentum in a collision follows directly from

  1. Newton's third law
  2. conservation of energy
  3. the law of gravitation
  4. Newton's first law only
Show answer and solution

Correct answer: A. Newton's third law

Equal-and-opposite internal forces (third law) make the total momentum change zero, so momentum is conserved.

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