Physics · Kinematics · chapter 3 of 14

Class 11 Physics Chapter 3: Motion in a Plane Assertion-reason questions with answers

2 assertion-reason questions on Motion in a Plane, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): The magnitude of the displacement of a body can never be greater than the length of the path it covers. Reason (R): The displacement of a body depends on the actual path it takes between two points.
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Answer: (c) A is true, but R is false.

A is true: displacement is the straight line joining the end points, so its magnitude is less than or equal to the path length. R is false: displacement depends only on the initial and final positions, not on the path.

Question 2
Assertion (A): The horizontal component of the velocity of a projectile remains constant during its flight. Reason (R): The time of flight of a projectile is twice the time it takes to reach its maximum height.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

A is true because the only acceleration, g, is vertical. R is also true (Tf = 2tm, from the symmetry of the path), but it is about the vertical motion and does not explain why the horizontal component is constant.

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