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Question #41591

Difficulty: 8/10 | 🟢 Free

The Question

Let u⃗,v⃗,w⃗\vec{u}, \vec{v}, \vec{w} be a right-handed system of mutually orthogonal unit vectors in R3\mathbb{R}^3. A family of curves C1C_1 in the plane spanned by u⃗\vec{u} and v⃗\vec{v} is given by the position vector r⃗=xu⃗+yv⃗\vec{r} = x\vec{u} + y\vec{v} satisfying the differential equation: dr⃗=(3x2[u⃗ r⃗ w⃗])u⃗+(2y[r⃗ u⃗ w⃗])v⃗d\vec{r} = \left( 3x^2 [\vec{u}\ \vec{r}\ \vec{w}] \right) \vec{u} + \left( 2y [\vec{r}\ \vec{u}\ \vec{w}] \right) \vec{v} where [a⃗ b⃗ c⃗][\vec{a}\ \vec{b}\ \vec{c}] denotes the scalar triple product. Let C2C_2 be the orthogonal trajectory of the family C1C_1 that passes through the point with position vector u⃗+5v⃗\vec{u} + 5\vec{v}. If the point 2u⃗+αv⃗2\vec{u} + \alpha\vec{v} lies on C2C_2, find the value of α2\alpha^2.

Options

  • A.

    16

  • B.

    18

  • C.

    24

  • D.

    32

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Bridge

Practice problems that bridge the gap between foundational theory and advanced practical application.

Concepts Behind This Question

Variable Separable Constraints|Orthogonal Trajectories|Linear Independence vs Dependence|Vector Product Anti-Commutativity

Why This Question Is Tricky

Common Mistakes

This question tests the intersection of vector calculus and differential equations.

The primary trap lies in the anti-commutativity of the scalar triple product (Concept 323).

Students often incorrectly assume [r⃗ u⃗ w⃗]=[u⃗ r⃗ w⃗][\vec{r}\ \vec{u}\ \vec{w}] = [\vec{u}\ \vec{r}\ \vec{w}], leading to a missing negative sign in the dydy component.

This results in an incorrect orthogonal trajectory equation (y2=−x3+26y^2 = -x^3 + 26) and a trap answer of 18.

Furthermore, equating the components of dr⃗d\vec{r} relies on the linear independence of the basis vectors u⃗\vec{u} and v⃗\vec{v} (Concept 321), ensuring a unique variable separable form.

Quick Facts About This Question

Question Information

SubjectMathematics
ChapterDifferential Equations - Class 12
ConceptVariable Separable Constraints
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree