Class 11 Physics DPP — Ch 4 — Laws of Motion | 22 July 2026

Assertion (A): A passenger jerks forward when a moving bus stops suddenly.
Reason (R): The lower body stops with the bus but the upper body continues in motion due to inertia.

Choose the correct option:

A. Both A and R are true, and R is the correct explanation of A B. Both A and R are true, but R is NOT the correct explanation of A C. A is true, but R is false D. A is false, but R is true

📝 SolutionWhen the bus stops, the upper body tends to keep moving due to inertia of motion, causing a forward jerk. R correctly explains A.

The law of conservation of momentum holds when the net external force is:

A. maximum B. zero C. increasing D. negative

📝 SolutionTotal momentum of a system is conserved only when the net external force acting on it is zero.

The recoil of a gun when fired is an example of Newton's:

A. first law B. second law C. third law D. law of inertia

📝 SolutionThe gun pushes the bullet forward (action) and the bullet pushes the gun back (reaction) — Newton's third law.

The force needed to keep a body moving at constant velocity on a frictionless surface is:

A. equal to its weight B. zero C. equal to its mass D. infinite

📝 SolutionWith no friction, no force is needed to maintain constant velocity (Newton's first law): the body continues on its own.

A body of mass 5 kg has momentum 20 kg·m/s. Its velocity is:

A. 2 m/s B. 4 m/s C. 5 m/s D. 100 m/s

📝 Solution$v = \frac{p}{m} = \frac{20}{5} = 4\ m/s$.

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Class 11 · Physics

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