Class CBSE Class 12 Mathematics Vector Algebra Q #1723
COMPETENCY BASED
APPLY
1 Marks 2026 AISSCE(Board Exam) MCQ SINGLE
If position vector $\vec{p}$ of a point (24, n) is such that $|\vec{p}|=25$, then the value of n is:
(A) $\pm 49$
(B) $\pm 5$
(C) $\pm 1$
(D) $\pm 7$
Correct Answer: D

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Detailed Solution

Step 1: Define the position vector

The position vector $\vec{p}$ of a point $(24, n)$ in a 2D plane is given by: $$ \vec{p} = 24\hat{i} + n\hat{j} $$

Step 2: Apply the magnitude formula

The magnitude of a vector $\vec{p} = x\hat{i} + y\hat{j}$ is given by $|\vec{p}| = \sqrt{x^2 + y^2}$. Given $|\vec{p}| = 25$, we have: $$ \sqrt{24^2 + n^2} = 25 $$

Step 3: Solve for n

Squaring both sides: $$ 24^2 + n^2 = 25^2 $$ $$ 576 + n^2 = 625 $$ $$ n^2 = 625 - 576 $$ $$ n^2 = 49 $$ $$ n = \pm \sqrt{49} = \pm 7 $$

Final Answer: \pm 7

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student must apply the standard formula for the magnitude of a vector to solve for an unknown coordinate.
Knowledge Dimension: PROCEDURAL
Justification: The question requires the execution of a specific mathematical algorithm (magnitude calculation) to reach the solution.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. This question tests the fundamental understanding of vector algebra and coordinate geometry integration, which is a core competency in the Vector Algebra unit.