Vector Algebra and Calculus Practice Quiz (11 questions)

All questions and answers

1. Which set of attributes defines a vector represented by a directed segment?

Origin, direction, and supporting line
Direction, supporting line, and point of application
Sense, magnitude, and point of application
Origin, direction, sense, and magnitude

Origin, direction, sense, and magnitude

Explanation

A vector is defined by its origin, direction, sense, and magnitude. A supporting line is not a defining attribute in this list, and point of application does not replace sense or magnitude.

2. A vector is known to have a direction, sense, and magnitude, but neither its supporting line nor its point of application is specified. How is it classified?

A directed segment with a specified origin
A free vector
A bound vector
A sliding vector

A free vector

Explanation

A free vector has a specified direction, sense, and magnitude, while its supporting line and point of application are unspecified. A sliding vector has an unfixed point of application, and a bound vector has its elements determined.

3. A coordinate basis has pairwise perpendicular basis vectors, but one of those vectors has magnitude 2. Which description applies?

Neither orthogonal nor orthonormal
Direct, but not orthogonal
Orthogonal, but not orthonormal
Orthonormal, but not orthogonal

Orthogonal, but not orthonormal

Explanation

An orthonormal basis requires both mutual perpendicularity and unit magnitudes; this basis meets the perpendicularity condition but has a vector of magnitude 2. The misconception behind “orthonormal” is that perpendicularity alone is sufficient.

4. In a three-dimensional basis, a vector has components (−2,4,1)(-2, 4, 1). Which expression represents the vector?

2e⃗1+4e⃗2+e⃗32\vec{e}_1+4\vec{e}_2+\vec{e}_3
−2e⃗1+4e⃗2+e⃗3-2\vec{e}_1+4\vec{e}_2+\vec{e}_3
−2e⃗2+4e⃗1+e⃗3-2\vec{e}_2+4\vec{e}_1+\vec{e}_3
−2e⃗1+4e⃗2−e⃗3-2\vec{e}_1+4\vec{e}_2-\vec{e}_3

$$-2\vec{e}_1+4\vec{e}_2+\vec{e}_3$$

Explanation

A vector with components (x,y,z)(x,y,z) is expressed as xe⃗1+ye⃗2+ze⃗3x\vec{e}_1+y\vec{e}_2+z\vec{e}_3, so the components give the coefficients of their corresponding basis vectors. Omitting the negative sign changes the first component, while swapping basis vectors changes which component belongs to each direction.

5. What is the component-wise rule for adding two vectors in R3\mathbb{R}^3?

Multiply corresponding components to form a new vector.
Add the corresponding components to form a new vector.
Add the magnitudes while keeping the first vector's components.
Multiply each component of the first vector by the second vector's magnitude.

Add the corresponding components to form a new vector.

Explanation

Vector addition combines corresponding components, so the result is also a vector in R3\mathbb{R}^3. Multiplying corresponding components is not the stated rule for a vector sum.

6. When is a system of vectors linearly independent?

When the system contains a zero vector and all other vectors are nonzero
When a linear combination equal to the zero vector forces every coefficient to be zero
When each vector can be written as a linear combination of the remaining vectors
When a linear combination equal to the zero vector has at least one nonzero coefficient

When a linear combination equal to the zero vector forces every coefficient to be zero

Explanation

Linear independence means the zero-vector relation has only the trivial solution, with every coefficient equal to zero. A nonzero-coefficient relation instead establishes linear dependence.

7. What role does the dot product play in relating two vectors geometrically?

It gives a scalar equal to the product of their magnitudes and the cosine of the angle between them.
It gives a unit vector pointing along the direction of their sum.
It gives the distance between their endpoints, independent of their directions.
It gives a vector perpendicular to both, with magnitude based on the sine of their angle.

It gives a scalar equal to the product of their magnitudes and the cosine of the angle between them.

Explanation

The dot product is a scalar that combines the vectors’ magnitudes with the cosine of the angle between them. The perpendicular vector described by a sine-based magnitude is the role of the vector product, not the dot product.

8. How does an orthonormal set of vectors differ from an orthogonal set?

An orthonormal set has unit-length vectors that may be nonperpendicular, whereas an orthogonal set requires pairwise perpendicularity.
An orthonormal set has pairwise perpendicular vectors of unit length, whereas an orthogonal set requires pairwise perpendicularity.
An orthonormal set has pairwise perpendicular vectors with positive dot products, whereas an orthogonal set requires zero magnitudes.
An orthonormal set has pairwise perpendicular vectors of equal length, whereas an orthogonal set requires unit lengths.

An orthonormal set has pairwise perpendicular vectors of unit length, whereas an orthogonal set requires pairwise perpendicularity.

Explanation

Orthonormality combines perpendicularity with the requirement that each vector has magnitude one; orthogonality concerns perpendicularity. Equal lengths do not make an orthogonal set orthonormal unless those lengths are one.

9. What is the consequence of reversing the order of the two vectors in a vector product?

The resulting vector keeps its direction while its magnitude changes sign.
The resulting vector points in the opposite direction while keeping the same magnitude.
The resulting vector becomes parallel to both input vectors.
The resulting vector remains unchanged in both direction and magnitude.

The resulting vector points in the opposite direction while keeping the same magnitude.

Explanation

The vector product is antisymmetric, so swapping its inputs multiplies the result by −1-1 and reverses its direction. Its magnitude is unchanged because it depends on the magnitudes of the inputs and the sine of the angle between them.

10. To evaluate A⃗∧(B⃗∧C⃗)\vec{A}\wedge(\vec{B}\wedge\vec{C}) without first computing the inner vector product, which identity should you use?

A⃗(B⃗⋅C⃗)−C⃗(A⃗⋅B⃗)\vec{A}(\vec{B}\cdot\vec{C})-\vec{C}(\vec{A}\cdot\vec{B})
B⃗(A⃗⋅B⃗)−C⃗(A⃗⋅C⃗)\vec{B}(\vec{A}\cdot\vec{B})-\vec{C}(\vec{A}\cdot\vec{C})
C⃗(A⃗⋅B⃗)−B⃗(A⃗⋅C⃗)\vec{C}(\vec{A}\cdot\vec{B})-\vec{B}(\vec{A}\cdot\vec{C})
B⃗(A⃗⋅C⃗)−C⃗(A⃗⋅B⃗)\vec{B}(\vec{A}\cdot\vec{C})-\vec{C}(\vec{A}\cdot\vec{B})

$$\vec{B}(\vec{A}\cdot\vec{C})-\vec{C}(\vec{A}\cdot\vec{B})$$

Explanation

The double vector product can be rewritten as a linear combination of the two inner-product vectors, with coefficients given by the indicated dot products. The expression involving A⃗(B⃗⋅C⃗)\vec{A}(\vec{B}\cdot\vec{C}) is a different arrangement and does not give this identity.

11. Which expression gives the orthogonal projection of a vector V⃗\vec{V} onto a plane whose unit normal is n⃗\vec{n}?

V⃗−(V⃗∧n⃗)\vec{V}-(\vec{V}\wedge\vec{n})
(V⃗⋅n⃗)n⃗(\vec{V}\cdot\vec{n})\vec{n}
V⃗−(V⃗⋅n⃗)n⃗\vec{V}-(\vec{V}\cdot\vec{n})\vec{n}
n⃗−(V⃗⋅n⃗)V⃗\vec{n}-(\vec{V}\cdot\vec{n})\vec{V}

$$\vec{V}-(\vec{V}\cdot\vec{n})\vec{n}$$

Explanation

The projection into the plane removes the component of V⃗\vec{V} along its unit normal, giving V⃗−(V⃗⋅n⃗)n⃗\vec{V}-(\vec{V}\cdot\vec{n})\vec{n}. The expression (V⃗⋅n⃗)n⃗(\vec{V}\cdot\vec{n})\vec{n} is instead the projection onto the normal axis.

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Lock in the answers with 10 flashcards on Vector Algebra and Calculus.

What is a vector?

A directed segment defined by its origin, direction, sense, and magnitude.

What makes a basis orthonormal?

Its basis vectors are mutually perpendicular and each has magnitude 1.

What does the dot product of basis vectors e⃗i\vec{e}_i and e⃗j\vec{e}_j equal when i=ji=j?

1.

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