Chapter 2: Motion in a Straight Line Assertion-Reason Questions | physics Class 11 CBSE

Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 1

Logic Check

Assertion (A): The instantaneous speed of a particle at any instant is always equal to the magnitude of its instantaneous velocity. Reason (R): Over an infinitesimally small time interval, the path length and magnitude of displacement become equal.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): A particle thrown vertically upward has zero velocity at its highest point but non-zero acceleration. Reason (R): Acceleration due to gravity acts on the particle throughout its flight, regardless of its velocity.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): The average speed of an object over a finite interval of time is always greater than or equal to the magnitude of its average velocity. Reason (R): The magnitude of displacement is always greater than or equal to the path length.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): For uniformly accelerated motion, the position-time graph is a straight line. Reason (R): A straight line on the x-t graph implies constant velocity, i.e., zero acceleration.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): The area under the velocity-time graph between two time instants gives the displacement of the object. Reason (R): Displacement is the product of velocity and time, and for non-uniform velocity, the area under the v-t curve represents the integral of velocity over time.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 6

Logic Check

Assertion (A): The kinematic equations v = v0 + at, x = v0t + ½at², and v² = v0² + 2ax are always valid for any one-dimensional motion. Reason (R): These equations were derived assuming constant acceleration throughout the motion.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 7

Logic Check

Assertion (A): In free fall, the distances covered in successive equal time intervals are in the ratio 1:3:5:7:... Reason (R): This ratio arises because free fall is motion with uniform acceleration starting from rest.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): If a particle moves with constant speed in one dimension, its acceleration must be zero. Reason (R): In one-dimensional motion, constant speed means constant magnitude of velocity; since direction cannot change in 1D, velocity is constant, making acceleration zero.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 9

Logic Check

Assertion (A): Stopping distance is proportional to the square of the initial velocity of the vehicle. Reason (R): From v² = v0² + 2ax, with v = 0, stopping distance ds = v0²/(2a), which is proportional to v0².

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Velocity and acceleration cannot change abruptly at any instant in realistic physical motion. Reason (R): In any realistic situation, the functions describing position, velocity, and acceleration are differentiable (and hence continuous) at all points.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 11

Logic Check

Assertion (A): The sign of acceleration indicates whether the particle is speeding up or slowing down. Reason (R): Whether a particle speeds up or slows down depends on whether acceleration and velocity are in the same or opposite directions, not on the sign of acceleration alone.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 12

Logic Check

Assertion (A): For a round trip (returning to the starting point), the average velocity is zero. Reason (R): Average velocity is defined as total displacement divided by total time, and displacement is zero for a round trip.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): Reaction time increases stopping distance even when the braking deceleration is very large. Reason (R): During reaction time, the vehicle travels at its initial speed before deceleration begins, adding a reaction distance to the total stopping distance.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 14

Logic Check

Assertion (A): The velocity of object A relative to object B and the velocity of object B relative to object A are equal in magnitude and opposite in direction. Reason (R): vAB = vA – vB and vBA = vB – vA = –vAB, so vAB = –vBA.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): A spinning cricket ball that turns sharply on hitting the ground cannot be treated as a point object. Reason (R): The point object approximation is invalid when the size of the object is comparable to or significantly affects the phenomenon being studied.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 16

Logic Check

Assertion (A): For motion with constant acceleration, the average velocity equals the arithmetic mean of initial and final velocities: v̄ = (v0 + v)/2. Reason (R): For constant acceleration, velocity varies linearly with time, so the average of velocity over the interval equals the average of its values at the endpoints.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 17

Logic Check

Assertion (A): Instantaneous acceleration at any point on a velocity-time graph is the slope of the chord joining two nearby points. Reason (R): Instantaneous acceleration is defined as the limit of average acceleration as the time interval approaches zero, which equals the slope of the tangent to the v-t curve at that instant.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 18

Logic Check

Assertion (A): Two objects moving in the same direction with the same velocity have zero relative velocity. Reason (R): Relative velocity vAB = vA – vB. If vA = vB, then vAB = 0.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): The x-t graph for a freely falling body (taking downward as positive) starting from rest is a parabola opening upward. Reason (R): For free fall from rest, y = ½gt², which is a quadratic function of t, producing a parabola; since g > 0 and t² is always positive, the parabola opens upward.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 20

Logic Check

Assertion (A): The definitions of instantaneous velocity and acceleration are always exact and applicable to any motion. Reason (R): The kinematic equations (v = v0 + at, etc.) are exact and applicable to all types of motion, including variable acceleration.

Reasoning Options

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Chapter sections

Chapter 2: Motion in a Straight Line | Assertion-Reason

Assertion (A): The instantaneous speed of a particle at any instant is always equal to the magnitude of its instantaneous velocity. Reason (R): Over an infinitesimally small time interval, the path length and magnitude of displacement become equal.

Assertion (A): A particle thrown vertically upward has zero velocity at its highest point but non-zero acceleration. Reason (R): Acceleration due to gravity acts on the particle throughout its flight, regardless of its velocity.

Assertion (A): The average speed of an object over a finite interval of time is always greater than or equal to the magnitude of its average velocity. Reason (R): The magnitude of displacement is always greater than or equal to the path length.

Assertion (A): For uniformly accelerated motion, the position-time graph is a straight line. Reason (R): A straight line on the x-t graph implies constant velocity, i.e., zero acceleration.

Assertion (A): The area under the velocity-time graph between two time instants gives the displacement of the object. Reason (R): Displacement is the product of velocity and time, and for non-uniform velocity, the area under the v-t curve represents the integral of velocity over time.

Assertion (A): The kinematic equations v = v0 + at, x = v0t + ½at², and v² = v0² + 2ax are always valid for any one-dimensional motion. Reason (R): These equations were derived assuming constant acceleration throughout the motion.

Assertion (A): In free fall, the distances covered in successive equal time intervals are in the ratio 1:3:5:7:... Reason (R): This ratio arises because free fall is motion with uniform acceleration starting from rest.

Assertion (A): If a particle moves with constant speed in one dimension, its acceleration must be zero. Reason (R): In one-dimensional motion, constant speed means constant magnitude of velocity; since direction cannot change in 1D, velocity is constant, making acceleration zero.

Assertion (A): Stopping distance is proportional to the square of the initial velocity of the vehicle. Reason (R): From v² = v0² + 2ax, with v = 0, stopping distance ds = v0²/(2a), which is proportional to v0².

Assertion (A): Velocity and acceleration cannot change abruptly at any instant in realistic physical motion. Reason (R): In any realistic situation, the functions describing position, velocity, and acceleration are differentiable (and hence continuous) at all points.

Assertion (A): The sign of acceleration indicates whether the particle is speeding up or slowing down. Reason (R): Whether a particle speeds up or slows down depends on whether acceleration and velocity are in the same or opposite directions, not on the sign of acceleration alone.

Assertion (A): For a round trip (returning to the starting point), the average velocity is zero. Reason (R): Average velocity is defined as total displacement divided by total time, and displacement is zero for a round trip.

Assertion (A): Reaction time increases stopping distance even when the braking deceleration is very large. Reason (R): During reaction time, the vehicle travels at its initial speed before deceleration begins, adding a reaction distance to the total stopping distance.

Assertion (A): The velocity of object A relative to object B and the velocity of object B relative to object A are equal in magnitude and opposite in direction. Reason (R): vAB = vA – vB and vBA = vB – vA = –vAB, so vAB = –vBA.

Assertion (A): A spinning cricket ball that turns sharply on hitting the ground cannot be treated as a point object. Reason (R): The point object approximation is invalid when the size of the object is comparable to or significantly affects the phenomenon being studied.

Assertion (A): Two objects moving in the same direction with the same velocity have zero relative velocity. Reason (R): Relative velocity vAB = vA – vB. If vA = vB, then vAB = 0.

Assertion (A): The definitions of instantaneous velocity and acceleration are always exact and applicable to any motion. Reason (R): The kinematic equations (v = v0 + at, etc.) are exact and applicable to all types of motion, including variable acceleration.

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