Problem 2 - Master Resource Book in JEE Main Physics

Question

What is the numerical value of the vector \(3 \hat{\mathbf{i}}+4 \hat{\mathbf{j}}+4 \hat{\mathbf{k}}\) ? (a) \(3 \sqrt{2}\) (b) \(5 \sqrt{2}\) (c) \(7 \sqrt{2}\) (d) \(9 \sqrt{2}\)

Step-by-Step Solution

Answer

The numerical value is \(\sqrt{41}\), not provided in the options.

Step 1: Understand the Problem

We need to find the numerical value (magnitude) of the vector given by \(3 \hat{\mathbf{i}} + 4 \hat{\mathbf{j}} + 4 \hat{\mathbf{k}}\). This involves finding the magnitude of a three-dimensional vector.

Step 2: Use the Magnitude Formula

The formula to find the magnitude of a vector \(\mathbf{v} = a \hat{\mathbf{i}} + b \hat{\mathbf{j}} + c \hat{\mathbf{k}}\) is \(|\mathbf{v}| = \sqrt{a^2 + b^2 + c^2}\). We will use this formula to find the magnitude of the vector \(3 \hat{\mathbf{i}} + 4 \hat{\mathbf{j}} + 4 \hat{\mathbf{k}}\).

Step 3: Substitute Values Into Formula

Substitute \(a = 3\), \(b = 4\), and \(c = 4\) into the magnitude formula: \[|\mathbf{v}| = \sqrt{3^2 + 4^2 + 4^2}\]

Step 4: Calculate Squared Values

Calculate each component squared: \(3^2 = 9\), \(4^2 = 16\), and \(4^2 = 16\).

Step 5: Sum the Squared Values

Add the squared values found in Step 4: \[9 + 16 + 16 = 41\]

Step 6: Find the Square Root

Find the square root of the sum obtained in Step 5: \[|\mathbf{v}| = \sqrt{41}\]

Step 7: Compare and Select the Correct Answer

Compare \(\sqrt{41}\) to the choices given. Since there's no option \(\sqrt{41}\), we need to check if \(\sqrt{41}\) matches any provided choices when simplified further, but since there's no straightforward match, \(9\sqrt{2}\) is incorrect based on simple estimation. The provided options don't fit \(\sqrt{41}\). Hence, either re-evaluate the interpretation or check for color options after recomputing.

Key Concepts

Three-Dimensional Vector

A three-dimensional vector is one that exists in a space defined by three axes: the x-axis, y-axis, and z-axis. It is often used to represent quantities that have both magnitude and direction in this three-dimensional space, like force or velocity.

For instance, the vector given in the original problem is \(3 \hat{\mathbf{i}} + 4 \hat{\mathbf{j}} + 4 \hat{\mathbf{k}}\). Here, the components 3, 4, and 4 represent the vector's influence along the x, y, and z axes, respectively. Each component can either be positive or negative, indicating the direction along each axis.

• \(\hat{\mathbf{i}}\), \(\hat{\mathbf{j}}\), and \(\hat{\mathbf{k}}\) are unit vectors in the direction of the x, y, and z axes.
• The three-dimensional nature means the vector is a point on or in a spatial plane.

Understanding this helps visualize how forces, lines, or movements occur in real-world 3D spaces. This concept is integral to physics and engineering applications.

Magnitude Formula

The magnitude formula is used to determine the size or length of a vector without considering its direction. It is particularly useful when you need to understand how much of a quantity is present.

For a vector \(\mathbf{v} = a \hat{\mathbf{i}} + b \hat{\mathbf{j}} + c \hat{\mathbf{k}}\), its magnitude \(|\mathbf{v}|\) is found using the magnitude formula:
\[|\mathbf{v}| = \sqrt{a^2 + b^2 + c^2}\]

• This formula is derived from the Pythagorean theorem, which applies in three-dimensional spaces too.
• It adds the squares of each vector component, reflecting the contribution of each dimension.

This equation helps measure the "overall size" of effects like speed or force without being distracted by the vector's specific orientation.

Vector Components

Vector components are the individual projections of a vector along the axes of a coordinate system. This decomposition of a vector into its components is a crucial skill in physics and mathematics.

The vector \(3 \hat{\mathbf{i}} + 4 \hat{\mathbf{j}} + 4 \hat{\mathbf{k}}\) has three main components:

• The \(3 \hat{\mathbf{i}}\) component, which indicates a projection of length 3 along the x-axis.
• The \(4 \hat{\mathbf{j}}\) component along the y-axis.
• The \(4 \hat{\mathbf{k}}\) component along the z-axis.

These components are the building blocks that help us reconstruct the full vector by understanding its influence and magnitude in each direction. They allow for the simplification of vector analysis, enabling complex system simulations in computations, whether it’s analyzing motion, fields, or forces.

Euclidean Norm

The Euclidean norm, also referred to as the L2 norm or simply the 'norm', is a commonly used measure of vector magnitude. It shows the distance of a vector from the origin to its endpoint in multi-dimensional spaces.

This measurement is essentially the same as the magnitude for a three-dimensional vector and is calculated with the formula:
\[ |\mathbf{v}| = \sqrt{a^2 + b^2 + c^2} \]

• It acts as the "straight-line" distance between two points, one being the origin.
• It is intuitive, as it mirrors real-world concepts of distance.

The Euclidean norm helps quantify how far 'along' a vector extends from its start, which is crucial for understanding movement and scale in 3D models or any physics simulation.