Chapter 4: Laws of Motion Assertion-Reason Questions | physics Class 11 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): A body moving with uniform velocity on a horizontal surface has zero net external force acting on it. Reason (R): According to Newton's First Law, zero acceleration implies zero net external force.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 2

Logic Check

Assertion (A): Aristotle's view that a force is required to keep a body in uniform motion is correct. Reason (R): In the real world, friction and viscous forces always oppose motion and must be overcome by applied force.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 3

Logic Check

Assertion (A): The momentum of an isolated system is conserved. Reason (R): For an isolated system, the net external force is zero, so the rate of change of total momentum is zero.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): Action and reaction forces cancel each other and produce no net effect. Reason (R): Action and reaction forces are equal in magnitude and opposite in direction.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 5

Logic Check

Assertion (A): A cricketer draws his hands backward while catching a fast ball to reduce the force on his hands. Reason (R): By increasing the time of contact, the average force exerted on the hands is reduced for the same change in momentum.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 6

Logic Check

Assertion (A): Newton's Second Law is a vector law. Reason (R): It is equivalent to three independent scalar equations, one for each component of the force and acceleration vectors.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): When a ball thrown vertically upward reaches its highest point, its velocity is zero, so the net force on it is also zero at that instant. Reason (R): The gravitational force mg acts downward on the ball at all points of its trajectory, including the highest point.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 8

Logic Check

Assertion (A): The coefficient of kinetic friction is always less than the coefficient of static friction for the same pair of surfaces. Reason (R): Once a body starts sliding, the frictional force decreases from the maximum static value to the kinetic value.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 9

Logic Check

Assertion (A): The normal reaction and the weight of a book resting on a table constitute an action-reaction pair. Reason (R): They are equal and opposite forces, so they form a Newton's Third Law pair.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 10

Logic Check

Assertion (A): A passenger in a bus is thrown forward when the bus suddenly brakes. Reason (R): Due to inertia, the passenger's body tends to continue with the velocity it had before the brakes were applied.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 11

Logic Check

Assertion (A): For a car taking a circular turn on a level road, the centripetal force is a new additional force acting on the car. Reason (R): The centripetal force is provided by static friction between the tyres and the road, which is an existing contact force.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): On a banked road, the maximum safe speed for a vehicle is greater than on a flat road of the same radius with the same coefficient of friction. Reason (R): On a banked road, both the horizontal component of normal reaction and friction contribute to the centripetal force.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 13

Logic Check

Assertion (A): Impulse and momentum have the same dimensions. Reason (R): Impulse equals the change in momentum of a body.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 14

Logic Check

Assertion (A): Static friction is a self-adjusting force. Reason (R): Static friction adjusts its magnitude to be equal and opposite to the applied force, up to its maximum limiting value.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The angle of repose of a body on an inclined plane is independent of the mass of the body. Reason (R): The coefficient of static friction depends only on the nature of the pair of surfaces in contact, not on the mass.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 16

Logic Check

Assertion (A): When a gun fires a bullet, the gun recoils backward with the same momentum as the bullet but in the opposite direction. Reason (R): By Newton's Third Law, the force on the bullet by the gun is equal and opposite to the force on the gun by the bullet, acting for the same time.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): All contact forces in mechanics (friction, normal reaction, tension) ultimately arise from gravitational force. Reason (R): At the microscopic level, contact forces arise from electrical forces between charged constituents of matter.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 18

Logic Check

Assertion (A): A body can be in equilibrium even when multiple forces act on it. Reason (R): Equilibrium requires that the vector sum of all forces acting on the body is zero, not that no forces act.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): An astronaut separated from an accelerating spaceship in interstellar space immediately has zero acceleration. Reason (R): With no nearby massive bodies and negligible gravitational pull from the spaceship, the net force on the astronaut is zero.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 20

Logic Check

Assertion (A): Rolling friction is larger than sliding friction for the same pair of surfaces. Reason (R): During rolling, the surfaces in contact are momentarily deformed, creating a finite contact area that opposes motion.

Reasoning Options

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Chapter sections

Chapter 4: Laws of Motion | Assertion-Reason

Assertion (A): A body moving with uniform velocity on a horizontal surface has zero net external force acting on it. Reason (R): According to Newton's First Law, zero acceleration implies zero net external force.

Assertion (A): Aristotle's view that a force is required to keep a body in uniform motion is correct. Reason (R): In the real world, friction and viscous forces always oppose motion and must be overcome by applied force.

Assertion (A): The momentum of an isolated system is conserved. Reason (R): For an isolated system, the net external force is zero, so the rate of change of total momentum is zero.

Assertion (A): Action and reaction forces cancel each other and produce no net effect. Reason (R): Action and reaction forces are equal in magnitude and opposite in direction.

Assertion (A): A cricketer draws his hands backward while catching a fast ball to reduce the force on his hands. Reason (R): By increasing the time of contact, the average force exerted on the hands is reduced for the same change in momentum.

Assertion (A): Newton's Second Law is a vector law. Reason (R): It is equivalent to three independent scalar equations, one for each component of the force and acceleration vectors.

Assertion (A): When a ball thrown vertically upward reaches its highest point, its velocity is zero, so the net force on it is also zero at that instant. Reason (R): The gravitational force mg acts downward on the ball at all points of its trajectory, including the highest point.

Assertion (A): The coefficient of kinetic friction is always less than the coefficient of static friction for the same pair of surfaces. Reason (R): Once a body starts sliding, the frictional force decreases from the maximum static value to the kinetic value.

Assertion (A): The normal reaction and the weight of a book resting on a table constitute an action-reaction pair. Reason (R): They are equal and opposite forces, so they form a Newton's Third Law pair.

Assertion (A): A passenger in a bus is thrown forward when the bus suddenly brakes. Reason (R): Due to inertia, the passenger's body tends to continue with the velocity it had before the brakes were applied.

Assertion (A): For a car taking a circular turn on a level road, the centripetal force is a new additional force acting on the car. Reason (R): The centripetal force is provided by static friction between the tyres and the road, which is an existing contact force.

Assertion (A): On a banked road, the maximum safe speed for a vehicle is greater than on a flat road of the same radius with the same coefficient of friction. Reason (R): On a banked road, both the horizontal component of normal reaction and friction contribute to the centripetal force.

Assertion (A): Impulse and momentum have the same dimensions. Reason (R): Impulse equals the change in momentum of a body.

Assertion (A): Static friction is a self-adjusting force. Reason (R): Static friction adjusts its magnitude to be equal and opposite to the applied force, up to its maximum limiting value.

Assertion (A): The angle of repose of a body on an inclined plane is independent of the mass of the body. Reason (R): The coefficient of static friction depends only on the nature of the pair of surfaces in contact, not on the mass.

Assertion (A): When a gun fires a bullet, the gun recoils backward with the same momentum as the bullet but in the opposite direction. Reason (R): By Newton's Third Law, the force on the bullet by the gun is equal and opposite to the force on the gun by the bullet, acting for the same time.

Assertion (A): All contact forces in mechanics (friction, normal reaction, tension) ultimately arise from gravitational force. Reason (R): At the microscopic level, contact forces arise from electrical forces between charged constituents of matter.

Assertion (A): A body can be in equilibrium even when multiple forces act on it. Reason (R): Equilibrium requires that the vector sum of all forces acting on the body is zero, not that no forces act.

Assertion (A): An astronaut separated from an accelerating spaceship in interstellar space immediately has zero acceleration. Reason (R): With no nearby massive bodies and negligible gravitational pull from the spaceship, the net force on the astronaut is zero.

Assertion (A): Rolling friction is larger than sliding friction for the same pair of surfaces. Reason (R): During rolling, the surfaces in contact are momentarily deformed, creating a finite contact area that opposes motion.

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