Question:medium

A vector \(\sqrt{3}\hat{i} + \hat{j}\) rotates about its tail through an angle 30\(^\circ\) in clock wise direction then the new vector is

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Always check the magnitude first. The magnitude must remain 2. Options (c) and (d) have magnitudes 1 and can be eliminated immediately.
Updated On: Apr 22, 2026
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Solution and Explanation

Step 1: Understanding the Concept:
When a vector rotates, its magnitude remains unchanged, but its direction (angle with the axes) changes. We can solve this by finding the initial angle of the vector and adjusting it by the rotation angle.
Step 2: Key Formula or Approach:
1. Magnitude $|\vec{A}| = \sqrt{x^2 + y^2}$.
2. Initial angle $\theta = \tan^{-1}(y/x)$.
3. New vector $\vec{A'} = |A|\cos(\theta')\hat{i} + |A|\sin(\theta')\hat{j}$.
Step 3: Detailed Explanation:
1. Find Magnitude: \[ |\vec{A}| = \sqrt{(\sqrt{3})^2 + 1^2} = \sqrt{3 + 1} = 2 \]
2. Find Initial Angle: \[ \tan \theta = \frac{1}{\sqrt{3}} \implies \theta = 30^\circ \text{ (with the positive x-axis)} \]
3. Apply Rotation: The vector is at 30° and rotates 30° clockwise. \[ \text{New angle } \theta' = 30^\circ - 30^\circ = 0^\circ \]
4. Find New Vector: The vector now lies entirely along the positive x-axis. \[ \vec{A'} = 2 \cos(0^\circ)\hat{i} + 2 \sin(0^\circ)\hat{j} = 2(1)\hat{i} + 0 = 2\hat{i} \]
Step 4: Final Answer
The new vector is $2\hat{i}$.
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