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Vector Practice Test 5 ( Vector Product )
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1 / 50
If A = 2i and B = 3j, then A × B is
Standard unit vectors follow i × j = k. Here A × B = (2i) × (3j) = 6 (i × j). So A × B = 6k.
2 / 50
If we have two vectors A and B and |A| ≠ |B| and |A × B| = |A · B|, then:
Explanation:
3 / 50
What is the torque of a force F = (2î – 3ĵ + 4k̂) newton acting at a point r = (3î + 2ĵ + 3k̂) metre about the origin? (Given: τ = r × F)
4 / 50
The vector product of two parallel non-zero vectors is
For parallel vectors, the angle between them is 0°. Sine of 0° is zero. So |A × B| = |A||B| sin0° = 0, meaning the cross product is the zero vector.
5 / 50
If A = 1î + 2ĵ + 3k̂ and B = 2î + 4ĵ + 6k̂, then A × B = ?
B is 2·A (parallel to A), so A × B = 0 for any parallel vectors.
6 / 50
Which one of the following statements about vector product is correct?
Cross product is defined to give a new vector quantity. This new vector is perpendicular to the plane containing the original two vectors. So the result of A × B is always a vector, not a scalar.
7 / 50
The vector product (cross product) of two vectors A and B is defined as a vector whose magnitude is
For vectors A and B with angle θ between them, the cross product magnitude is given by |A × B|. By definition, |A × B| = |A||B| sinθ. So the magnitude depends on both magnitudes and sine of the included angle.
8 / 50
The scalar and vector product of two vectors, a = (3î – 4ĵ + 5k̂) and b = (–2î + ĵ – 3k̂) is equal to:
9 / 50
If A × B = 0, which of the following must be true?
Cross product is zero if vectors are parallel (θ = 0° or 180°) or if either vector is a zero vector. Because sin0° = sin180° = 0.
10 / 50
If A is a non-zero vector and λ is a scalar, then A × (λA) equals
Vector A and λA have the same or opposite direction depending on sign of λ. So they are parallel or antiparallel vectors. Cross product of parallel vectors is zero, hence A × (λA) is zero vector.
11 / 50
If A × B = 0 for non-zero vectors A and B, then
Cross product magnitude is |A × B| = |A||B| sinθ. If A and B are non-zero and A × B = 0, then sinθ must be zero. Sine becomes zero at θ = 0° or 180°, meaning the vectors are parallel or antiparallel.
12 / 50
The direction of A × B is
Cross product produces a vector that is normal to the plane of the two vectors. This new vector is at right angle to both A and B. So the direction of A × B is perpendicular to the plane containing A and B.
13 / 50
The vector product of two vectors is maximum when the angle between them is
Magnitude of cross product is |A × B| = |A||B| sinθ. This is maximum when sinθ is maximum. Sine has maximum value 1 at θ = 90°, so cross product is maximum at 90°.
14 / 50
The magnitude of torque τ = r × F is equal to
Torque magnitude is |τ| = |r × F|. By cross product definition, |r × F| = r F sinθ. Here θ is the angle between r and F.
15 / 50
A and B are two vectors and θ is the angle between them. If |A × B| = √3 (A · B), then the value of θ will be:
|A × B| = |A| |B| sin θ A · B = |A| |B| cos θ
Given: |A| |B| sin θ = √3 (|A| |B| cos θ) ⇒ sin θ = √3 cos θ ⇒ tan θ = √3 ⇒ θ = 60°
16 / 50
If the angle between vectors A and B is θ, the value of the product (B × A) · A is equal to:
The vector (B × A) is perpendicular to both B and A. So when we take the **dot product** of (B × A) with A, the result is:
(B × A) · A = 0
Reason: dot product of two perpendicular vectors is zero.
17 / 50
If i, j and k are unit vectors along x, y and z axes respectively, then j × i is
We know that i × j = k in right-handed system. Reversing the order gives j × i = −(i × j). So j × i = −k.
18 / 50
If A and B are two non-zero vectors such that |A × B| = |A||B|, then the angle between them is
From cross product magnitude, |A × B| = |A||B| sinθ. Given |A × B| equals |A||B|, so sinθ must be 1. Sine becomes 1 at θ = 90°, so the vectors are perpendicular.
19 / 50
The SI unit of the vector product of force and position vector (r × F) is the unit of
The vector r × F represents torque or moment of force. Force has unit newton and position vector has unit metre. So unit of torque is newton metre (N m).
20 / 50
Which of the following correctly expresses that vector product is not associative?
Associative law would require (A × B) × C to equal A × (B × C). For cross product these two expressions usually give different vectors. Therefore vector product does not satisfy associative law.
21 / 50
Which of the following combinations of two vectors will always give the largest possible magnitude of cross product |A × B| for fixed |A| and |B|?
Magnitude |A × B| = |A||B| sinθ depends on sine of angle between them. It is maximum when sinθ is maximum. Sine function reaches its maximum value 1 at 90°, so perpendicular vectors give largest |A × B|.
22 / 50
If A and B are two position vectors of adjacent vertices of a triangle, then ½|A × B| represents
Magnitude |A × B| gives area of parallelogram formed by A and B. A triangle formed by the same two vectors has half of this area. So ½|A × B| represents area of the triangle formed by A and B.
23 / 50
If |A| = 5, |B| = 7 and the angle between A and B is 90°, then |A × B| = ?
|A × B| = |A| |B| sin θ = 5 × 7 × sin 90° = 35.
24 / 50
The angle between vectors ( A x B ) & (B X A )
A × B = –(B × A) So, the two vectors are equal in magnitude but opposite in direction, hence the angle between them is π radians (180°).
25 / 50
For two vectors A and B, which of the following is correct?
Magnitude of vector product depends on sine of angle between vectors. By definition, |A × B| = |A||B| sinθ. So the cross product magnitude is proportional to sine of the included angle.
26 / 50
Given are two vectors, A = (2î – 5ĵ + 2k̂) and B = (4î – 10ĵ + ck̂). What should be the value of c so that vector A and B become parallel to each other?
27 / 50
Given vectors A = 2i + 3j + k and B = i – j + 4k, what is the vector A × B?
Calculate cross product using determinant:
28 / 50
Cross product of two vectors A and B represents which geometrical quantity in magnitude?
Magnitude |A × B| equals |A||B| sinθ. This is equal to the area of a parallelogram having sides A and B. So cross product magnitude represents area of the parallelogram formed by two vectors.
29 / 50
Which of the following option is not true, if vector A = 3î + 4ĵ and B = 6î + 8ĵ, where A and B are magnitudes of A and B?
A · B = 3×6 + 4×8 = 18 + 32 = 50 ❌ (not 48)
30 / 50
In three dimensions, the cross product of A = (Ax, Ay, Az) and B = (Bx, By, Bz) is given symbolically by
Vector product in components is written using a 3 × 3 determinant. First row contains unit vectors i, j, k. Second and third rows contain components of A and B respectively. Expanding this determinant gives the components of A × B.
31 / 50
If A, B and C are coplanar vectors, then the vector A × B is
If A, B and C are coplanar, they all lie in the same plane. Vector A × B is perpendicular to the plane containing A and B. Since C is also in that plane, A × B is perpendicular to C as well.
32 / 50
The direction of the vector A × B is given by:
The direction of the cross product vector is given by the right-hand rule: if fingers point along A and curl towards B, then the thumb points in the direction of A × B.
33 / 50
The right-hand rule for A × B states that
In the right-hand rule, you first point the fingers of your right hand along A. Then curl the fingers towards B through the smaller angle between them. Your extended thumb then points in the direction of A × B.
34 / 50
The value of the unit vector which is perpendicular to both A = î + 2ĵ + 3k̂ and B = î – 2ĵ – 3k̂ is equal to:
Its magnitude = √(6² + 4²) = √(36 + 16) = √52
35 / 50
If A, B and C are mutually perpendicular unit vectors, then (A × B) · C equals
Take A, B and C as i, j and k in a right-handed coordinate system. We know that i × j = k and k is a unit vector. Dot product of k with itself is 1. So (A × B) · C equals 1.
36 / 50
The cross product of two vectors A and B is:
The cross product A × B produces a vector that is perpendicular to both A and B following the right-hand rule. Its magnitude equals |A||B|sinθ, where θ is the angle between A and B.
37 / 50
The vector product î × k̂ equals:
Using right-hand rule / cyclic order î → ĵ → k̂, we have î × k̂ = –(k̂ × î) = –ĵ.
38 / 50
A student calculates the vector product of two vectors and gets a scalar answer. This indicates that
Cross product of two vectors should give a vector quantity. Dot product gives a scalar result. If the answer is scalar while calculating cross product, it means dot product formula was used by mistake.
39 / 50
Which algebraic property is NOT satisfied by vector product?
Cross product satisfies A × (B + C) = A × B + A × C, so distributive law holds. It also obeys (kA) × B = k(A × B), so scalar multiplication behaves well. But it is not commutative, because B × A = −(A × B). So the commutative law does not hold for vector product.
40 / 50
Which of the following is distributive over vector addition?
The cross product obeys distributive law over addition. So A × (B + C) expands as A × B plus A × C. Therefore A × (B + C) = A × B + A × C.
41 / 50
Which of the following is true about the vector product of two vectors?
Swapping the order in a cross product changes the sign of the result. So B × A equals −(A × B). This property is called anti-commutativity of the vector product.
42 / 50
Torque τ acting on a particle is defined as
Torque measures turning effect of a force about a point. By definition, torque is given by cross product of position vector r and force F. So τ = r × F.
43 / 50
If A = 3i + 4j and B = i, then A × B is
Compute A × B = (3i + 4j) × i. This equals 3(i × i) + 4(j × i). i × i is zero and j × i = −k. So A × B = 0 + 4(−k) = −4k.
44 / 50
If A × B is a zero vector, then which statement is correct?
Cross product magnitude is |A × B| = |A||B| sinθ. If |A × B| is zero, then either |A| or |B| is zero or sinθ is zero. Sinθ is zero when vectors are parallel or antiparallel. So cross product is zero if one vector is zero or the vectors are parallel.
45 / 50
The cross product of two vectors is closely related to which physical quantity in magnetic field problems?
Magnetic force on a moving charge is given by F = q v × B. Here v is velocity vector and B is magnetic field vector. This force is a vector product of charge velocity and magnetic field.
46 / 50
If two vectors a = 2î + ĵ and b = 3î + 2ĵ, then |a × b| = ?
47 / 50
The linear velocity of a rotating body is given by v = ω × r, where ω is the angular velocity and r is the radius vector. If ω = î − 2ĵ + 2k̂ and r = 4ĵ − 3k̂ then the value of |v| will be:
= î·[(-2)(-3) – (2·4)] – ĵ·[1·(-3) – (2·0)] + k̂·[1·4 – (-2·0)]
= î·(6 – 8) – ĵ·(-3 – 0) + k̂·(4 – 0)
= (–2)î + 3ĵ + 4k̂
|v| = √[(-2)² + 3² + 4²] = √[4 + 9 + 16] = √29
48 / 50
If two vectors A and B are perpendicular and have magnitudes 4 and 6 respectively, what is the magnitude of A × B?
Magnitude of cross product = |A||B|sinθSince vectors are perpendicular, θ = 90°, sin90° = 1.So magnitude = 4 × 6 × 1 = 24.
49 / 50
If for two vectors A and B, A × B = 0, then the vectors:
Two vectors will be parallel to each other.
50 / 50
What is the magnitude of the cross product A × B when A = 5 units, B = 3 units, and the angle between them is 90°?
Magnitude of cross product = |A||B|sinθ = 5 × 3 × sin90° = 15 × 1 = 15.
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