Laws of Motion — Class 11 MCQs with Answers

Laws of Motion — important questions & MCQs with answers (Class 11 Physics)

13 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 53 are timed and scored when you sign in.

1. Q1Easy

   Newton's first law is also called law of:

   A.Action-reaction

   B.Force

   C.Inertia✓ Correct

   D.Gravitation

   Answer: C. Inertia

   Explanation: Newton's first law is the law of inertia: with zero net force a body keeps its state of motion, at rest or moving. Action–reaction pairing is the third law, and force/gravitation are separate laws — the usual mix-up here.

2. Q2Easy

   Newton's First Law states a body remains at rest or in uniform motion unless:

   A.It is alive

   B.An external force acts on it✓ Correct

   C.Time passes

   D.Gravity acts

   Answer: B. An external force acts on it

   Explanation: Newton's first law (inertia) says a body stays at rest or keeps moving at constant velocity unless an external net force acts on it. It doesn't depend on being 'alive' or on time passing alone — only an unbalanced force changes its state.

3. Q3Easy

   Inertia is the:

   A.Force

   B.Acceleration

   C.Velocity

   D.Tendency to resist change in state of motion✓ Correct

   Answer: D. Tendency to resist change in state of motion

   Explanation: Inertia is a body's tendency to resist any change in its state of rest or motion — it's a property, not a force, velocity, or acceleration itself. A heavier trolley is harder to start or stop precisely because it has more inertia.

4. Q4Easy

   Linear momentum p = ?

   A.m + v

   B.mass × acceleration

   C.mv²

   D.mv✓ Correct

   Answer: D. mv

   Explanation: Linear momentum is defined as p = mv, e.g. a 2 kg ball at 3 m/s has p = 6 kg·m/s. It's mass times velocity (not mv², and not a sum m + v), and being a vector it points along the velocity direction.

5. Q5Easy

   Impulse J =

   A.F

   B.F · Δt = Δp✓ Correct

   C.ma

   D.mv²

   Answer: B. F · Δt = Δp

   Explanation: Impulse is defined as J = F·Δt, and equals the resulting change in momentum Δp — e.g. a 5 N force for 2 s gives an impulse of 10 N·s. It is not just force alone, nor ma or mv² — impulse pairs force with the time it acts.

6. Q6Medium

   Force on 5 kg mass with a = 3 m/s²:

   A.15 N✓ Correct

   B.5 N

   C.3 N

   D.1.7 N

   Answer: A. 15 N

   Explanation: Newton's second law gives F = ma: for a 5 kg mass accelerating at 3 m/s², F = 5 × 3 = 15 N. Reading off just the mass (5 N) or the acceleration (3 N) alone, without multiplying, is the tempting shortcut that misleads.

7. Q7Medium

   Force on 10 kg body giving acceleration 5 m/s²:

   A.50 N✓ Correct

   B.2 N

   C.15 N

   D.100 N

   Answer: A. 50 N

   Explanation: Newton's second law: F = ma = 10 kg × 5 m/s² = 50 N. Adding instead of multiplying (10 + 5 = 15 N) is the tempting slip that lands on the wrong distractor here.

8. Q8Medium

   Two carts (3 kg at 4 m/s and 2 kg at rest) on a smooth track. After collision (perfectly inelastic), velocity:

   A.2.4 m/s✓ Correct

   B.4 m/s

   C.2 m/s

   D.0 m/s

   Answer: A. 2.4 m/s

   Explanation: Momentum conservation for a perfectly inelastic collision: m₁v₁ = (m₁+m₂)v_f, so 3 kg × 4 m/s = 5 kg × v_f gives v_f = 12/5 = 2.4 m/s. Dividing by only one cart's mass instead of the combined 5 kg is what produces the wrong 4 m/s distractor.

9. Q9Medium

   Ball of 200 g hits wall at 10 m/s and rebounds at 10 m/s. Impulse:

   A.20 N·s

   B.2 N·s

   C.0

   D.4 N·s✓ Correct

   Answer: D. 4 N·s

   Explanation: Impulse equals the change in momentum: Δp = m(v_f − v_i) = 0.2 kg × (10 − (−10)) m/s = 4 N·s, taking the rebound velocity as negative since it reverses direction. Forgetting the sign flip on rebound, giving 10 − 10 = 0, is the common error.

10. Q10Medium

    Block of 5 kg on horizontal surface, μ_s = 0.4. Maximum static friction force (g = 10):

    A.5 N

    B.50 N

    C.2 N

    D.20 N✓ Correct

    Answer: D. 20 N

    Explanation: Maximum static friction is f_s = μ_s·mg = 0.4 × 5 kg × 10 m/s² = 20 N, using g = 10 m/s² as the problem implies. Forgetting to multiply by g, giving only μ_s × m = 2, produces a much smaller wrong-looking distractor.

11. Q11Hard

    Newton's third law: action-reaction pairs act on:

    A.Different bodies✓ Correct

    B.Same body

    C.Same direction

    D.At rest only

    Answer: A. Different bodies

    Explanation: Newton's third law pairs act on two different bodies — e.g. your hand pushes a table while the table pushes back on your hand — never on the same object. Forces cancelling on one body is a separate idea (equilibrium), not action–reaction.

12. Q12Hard

    A 4 kg and a 6 kg block are tied together and rest on a frictionless horizontal table. A string from the 6 kg block runs over a light frictionless pulley at the table edge and holds a 10 kg block hanging freely. Acceleration of the system (g = 10 m/s²):

    A.5 m/s²✓ Correct

    B.10 m/s²

    C.6.25 m/s²

    D.0 m/s²

    Answer: A. 5 m/s²

    Explanation: Only the hanging weight drives the system, but all three blocks share the acceleration: a = m_hang·g / m_total = (10×10)/(4+6+10) = 5 m/s². Answering 10 m/s² treats the hanging block as free-falling and ignores the 10 kg of table mass the string must also drag.

13. Q13Hard

    Object of mass m moves at v₀ and hits stationary object of mass m. After elastic collision:

    A.Move in opposite directions

    B.Both move at v₀/2

    C.Stick together

    D.First stops, second moves at v₀✓ Correct

    Answer: D. First stops, second moves at v₀

    Explanation: In an elastic collision between equal masses where one starts at rest, the incoming mass transfers all its momentum and kinetic energy to the target: the first mass stops and the second moves off at v₀. Both moving at v₀/2 describes an inelastic collision instead.

Laws of Motion — FAQs

More Class 11 Physics chapters

• 01Physical World
• 02Units and Measurements
• 03Motion in a Straight Line
• 04Motion in a Plane
• 06Work, Energy and Power
• 07System of Particles and Rotational Motion

Class 11 — other subjects

• Class 11 Biology chapters
• Class 11 Chemistry chapters
• Class 11 Computer Science chapters
• Class 11 English chapters
• Class 11 Mathematics chapters