The NCERT Solutions for Class 12 Maths Chapter 10 Vector Algebra are given here where the students learn about the difference between a scalar and a vector quantity, their properties, operations of vectors etc. The topic has an important role in helping the students score high marks not only in the board exams but also the competitive exams.
It is important to be prepared for the various problems asked during the 12th board examination. Solving through different exercises and problem sets give students the confidence to write the exams better. These class 12 NCERT solutions for Vector Algebra are very easy to understand. Students can also avail these NCERT solutions and download it for free to practice them offline as well.
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NCERT Solutions for Class 12 Maths Chapter 10 â€“ Vector Algebra
Exercise 10.1 Page No: 428
1. Represent graphically a displacement of 40 km, 30Â° east of north.
Solution:
The vector
represents the displacement of 40 km, 30^{o} east of north.
2. Classify the following measures as scalars and vectors.
(i) 10 kg (ii) 2 metres northwest (iii) 40Â°
(iv) 40 watt (v) 10^{â€“19}Â coulomb (vi) 20 m/s^{2}
Solution:
(i) 10 kg is a scalar quantity because it has only magnitude.
(ii) 2 meters northwest is a vector quantity as it has both magnitude and direction.
(iii) 40Â° is a scalar quantity as it has only magnitude.
(iv) 40 watts is a scalar quantity as it has only magnitude.
(v) 10^{â€“19}Â coulomb is a scalar quantity as it has only magnitude.
(vi) 20 m/s^{2}Â is a vector quantity as it has both magnitude and direction.
3. Classify the following as scalar and vector quantities.
(i) time period (ii) distance (iii) force
(iv) velocity (v) work done
Solution:
(i) Time period is a scalar quantity as it has only magnitude.
(ii) Distance is a scalar quantity as it has only magnitude.
(iii) Force is a vector quantity as it has both magnitude and direction.
(iv) Velocity is a vector quantity as it has both magnitude as well as direction.
(v) Work done is a scalar quantity as it has only magnitude.
4. In Figure, identify the following vectors.
(i) Coinitial (ii) Equal (iii) Collinear but not equal
Solution:
directions are not the same.
5. Answer the following as true or false.
(i)Â Â andare collinear.
(ii) Two collinear vectors are always equal in magnitude.
(iii) Two vectors having same magnitude are collinear.
(iv) Two collinear vectors having the same magnitude are equal.
Solution:
(i) True.
VectorsÂ
Â and
are parallel to the same line.
(ii) False.
Collinear vectors are those vectors that are parallel to the same line.
(iii) False.
Two vectors having the same magnitude need not necessarily be parallel to the same line.
(iv) False.
Only if the magnitude and direction of two vectors are the same, regardless of the positions of their initial points the two vector are said to be equal.
Exercise 10.2 Page No: 440
1. Compute the magnitude of the following vectors:
Solution:
Given vectors are:
2. Write two different vectors having same magnitude.
Solution:
3. Write two different vectors having same direction.
Solution:
4. Find the values ofÂ xÂ andÂ yÂ so that the vectorsÂ are equal
Solution:
Given vectorsÂ
will be equal only if their corresponding components are equal.
Thus, the required values ofÂ xÂ andÂ yÂ are 2 and 3 respectively.
5. Find the scalar and vector components of the vector with initial point (2, 1) and terminal point (â€“5, 7).
Solution:
The vector with initial point P (2, 1) and terminal point Q (â€“5, 7) can be shown as,
Thus, the required scalar components are â€“7 and 6 while the vector components areÂ
6. Find the sum of the vectors
Solution:
7. Find the unit vector in the direction of the vector
Solution:
8. Find the unit vector in the direction of vector , where P and Q are the points
(1, 2, 3) and (4, 5, 6), respectively
Solution:
9. For given vectors,Â andÂ , find the unit vector in the direction of the vectorÂ
Solution:
10. Find a vector in the direction of vectorÂ which has magnitude 8 units.
Solution:
11. Show that the vectorsare collinear.
Solution:
Therefore, the given vectors are collinear.
12. Find the direction cosines of the vectorÂ
Solution:
13. Find the direction cosines of the vector joining the points A (1, 2, â€“3) and
B (â€“1, â€“2, 1) directed from A to B.
Solution:
Given points are A (1, 2, â€“3) and B (â€“1, â€“2, 1).
Now,
14. Show that the vectorÂ is equally inclined to the axes OX, OY, and OZ.
Solution:
15. Find the position vector of a point R which divides the line joining two points P and Q whose position vectors areÂ Â respectively, in the ration 2:1
(i) internally
(ii) externally
Solution:
The position vector of point R dividing the line segment joining two points
P and Q in the ratioÂ m:Â nÂ is given by:
16. Find the position vector of the mid point of the vector joining the points P (2, 3, 4) and Q (4, 1, â€“ 2).
Solution:
The position vector of midpoint R of the vector joining points P (2, 3, 4) and Q (4, 1, â€“ 2) is given by,
17. Show that the points A, B and C with position vectors,,Â respectively form the vertices of a right angled triangle.
Solution:
Given position vectors of points A, B, and C are:
18. In triangle ABC (Fig 10.18) which of the following isÂ notÂ true:
Solution:
19. IfÂ are two collinear vectors, then which of the following areÂ incorrect:
A.Â , for some scalar Î»
B.Â
C.Â the respective components ofÂ are proportional
D.Â both the vectorsÂ have same direction, but different magnitudes
Solution:
Exercise 10.3 Page No: 447
1. Find the angle between two vectorsandwith magnitudes âˆš3 and 2, respectively having.
Solution:
2. Find the angle between the vectors
Solution:
3. Find the projection of the vectoron the vector.
Solution:
4. Find the projection of the vectoron the vector.
Solution:
5. Show that each of the given three vectors is a unit vector:
Also, show that they are mutually perpendicular to each other.
Solution:
6. Find
Solution:
7. Evaluate the product
Solution:
8. Find the magnitude of two vectors, having the same magnitude and such that the angle between them is 60Â° and their scalar product is Â½.
Solution:
9. Find, if for a unit vector
Solution:
10. Ifare such thatis perpendicular to, then find the value ofÂ Î».
Solution:
11. Show thatÂ is perpendicular to, for any two nonzero vectors.
Solution:
12. If, then what can be concluded about the vector?
Solution:
13. IfÂ are unit vectors such thatÂ , find the value ofÂ .
Solution:
14. If either vector, then. But the converse need not be true. Justify your answer with an example.
Solution:
15. If the vertices A, B, C of a triangle ABC are (1, 2, 3), (â€“1, 0, 0), (0, 1, 2), respectively, then find âˆ ABC. [âˆ ABC is the angle between the vectorsand]
Solution:
16. Show that the points A (1, 2, 7), B (2, 6, 3) and C (3, 10, â€“1) are collinear.
Solution:
Given points are A (1, 2, 7), B (2, 6, 3), and C (3, 10, â€“1).
Now,
Therefore, the given points A, B, and C are collinear.
17. Show that the vectorsform the vertices of a right angled triangle.
Solution:
18. Ifis a nonzero vector of magnitude â€˜aâ€™ and Î» a nonzero scalar, thenÂ Î»is unit vector if
Solution:
Exercise 10.4 Page No: 454
1. Find, ifÂ and
Solution:
We have,
2. Find a unit vector perpendicular to each of the vectorÂ and, whereÂ and.
Solution:
We have,
3. If a unit vectorÂ Â makes an angleswithÂ withÂ and an acute angleÂ Î¸Â with, then findÂ Î¸Â and hence, the compounds of.
Solution:
4. Show that
Solution:
Taking the LHS, we have
5. FindÂ Î»Â andÂ Î¼Â ifÂ .
Solution:
6. Given thatÂ Â and. What can you conclude about the vectors?
Solution:
Given,
7. Let the vectorsÂ given asÂ . Then show thatÂ
Solution:
We have,
8. If eitherÂ Â or, then. Is the converse true? Justify your answer with an example.
Solution:
9. Find the area of the triangle with vertices A (1, 1, 2), B (2, 3, 5) and C (1, 5, 5).
Solution:
10. Find the area of the parallelogram whose adjacent sides are determined by the vectorÂ .
Solution:
11. Let the vectorsÂ andÂ be such thatÂ and, thenÂ is a unit vector, if the angle betweenÂ andÂ is
Solution:
12. Area of a rectangle having vertices A, B, C, and D with position vectorsÂ andÂ Â respectively is
Solution:
Miscellaneous Exercise Page No: 458
1. Write down a unit vector in XYplane, making an angle of 30Â° with the positive direction ofÂ xaxis.
Solution:
2. Find the scalar components and magnitude of the vector joining the points P (x_{1}, y_{1}, z_{1}) and Q (x_{2}, y_{2}, z_{2}).
Solution:
3. A girl walks 4 km towards west, then she walks 3 km in a direction 30Â° east of north and stops. Determine the girlâ€™s displacement from her initial point of departure.
Solution:
Let O and B be the initial and final positions of the girl respectively.
Then, the girlâ€™s position can be shown as:
4. If, then is it true that? Justify your answer.
Solution:
5. Find the value ofÂ xÂ for whichis a unit vector.
Solution:
6. Find a vector of magnitude 5 units, and parallel to the resultant of the vectors
.
Solution:
7. If, find a unit vector parallel to the vector.
Solution:
8. Show that the points A (1, â€“2, â€“8), B (5, 0, â€“2) and C (11, 3, 7) are collinear, and find the ratio in which B divides AC.
Solution:
9. Find the position vector of a point R which divides the line joining two points P and Q whose position vectors areexternally in the ratio 1: 2. Also, show that P is the mid point of the line segment RQ.
Solution:
10. The two adjacent sides of a parallelogram areandÂ .
Find the unit vector parallel to its diagonal. Also, find its area.
Solution:
11. Show that the direction cosines of a vector equally inclined to the axes OX, OY and OZ are.
Solution:
Letâ€™s assume a vector to be equally inclined to axes OX, OY, and OZ at angleÂ Î±.
Then, the direction cosines of the vector are cosÂ Î±, cosÂ Î±, and cosÂ Î±.
Now, we know that
Therefore, the direction cosines of the vector which are equally inclined to the axes are
.
12. LetÂ and. Find a vectorÂ which is perpendicular to bothÂ and, and.
Solution:
13. The scalar product of the vectorwith a unit vector along the sum of vectorsÂ andÂ is equal to one. Find the value of Î».
Solution:
14. IfÂ are mutually perpendicular vectors of equal magnitudes, show that the vectorÂ is equally inclined toÂ and.
Solution:
15. Prove that, if and only ifÂ are perpendicular, given.
Solution:
16. IfÂ Î¸Â is the angle between two vectorsÂ andÂ , thenÂ only when
Solution:
17. LetÂ Â andÂ Â be two unit vectors andÎ¸Â is the angle between them. ThenÂ is a unit vector if
Solution:
18. The value ofÂ is
(A) 0 (B) â€“1 (C) 1 (D) 3
Solution:
Given,
The correct answer is C.
19. IfÂ Î¸Â is the angle between any two vectorsÂ and, thenÂ whenÂ Î¸ is equal to
Solution:
The major concepts of Maths covered in Chapter 10 Vector Algebra of NCERT Solutions for Class 12 includes:
10.1 Introduction
10.2 Basic Concepts

 Position Vector
 Direction Cosines
10.3 Types of Vectors

 Zero Vector
 Unit Vector
 Coinitial Vectors
 Collinear Vectors
 Equal Vectors
 Negative of a Vector
10.4 Addition of Vectors

 Properties of vector addition
10.5 Multiplication of a Vector by a Scalar
10.5.1 Components of a vector
10.5.2 Vector joining two points
10.5.3 Section formula
10.6 Product of Two Vectors
10.6.1 Scalar (or dot) product of two vectors
10.6.2 Projection of a vector on a line
10.6.3 Vector (or cross) product of two vectors
Exercise 10.1 Solutions 5 Questions
Exercise 10.2 Solutions 19 Questions
Exercise 10.3 Solutions 18 Questions
Exercise 10.4 Solutions 12 Questions
Miscellaneous Exercise On Chapter 10 Solutions 19 Questions
NCERT Solutions for Class 12 Maths Chapter 10 Vector Algebra
The chapter Vector Algebra belongs to the unit Vectors and Three â€“ Dimensional Geometry, that adds up to 14 marks of the total marks. There are 4 exercises along with a miscellaneous exercise in this chapter to help students understand the concepts related to Vectors and Vector Algebra clearly. Some of the topics discussed in the tenth Chapter of NCERT Solutions for Class 12 Maths are as follows:
 The scalar components of a vector are its direction ratios, and represent its projections along the respective axes.
 The magnitude (r), direction ratios (a, b, c) and direction cosines (l, m, n) of any vector are related as l=(a/r), m=(b/r) n=(c/r)
 The vector sum of the three sides of a triangle taken in order is 0.
 The vector sum of two coinitial vectors is given by the diagonal of the parallelogram whose adjacent sides are the given vectors.
 The multiplication of a given vector by a scalar Î», changes the magnitude of the vector by the multiple Î», and keeps the direction same (or makes it opposite) according as the value of Î» is positive (or negative).
The other concepts and topics explained in the chapter can be understood by going through the Chapter 10 of the NCERT textbook for class 12.
Key Features of NCERT Solutions for Class 12 Maths Chapter 10 Vector Algebra
Studying the Vector Algebra of Class 12 enables the students to understand the following:
Vectors and scalars, magnitude and direction of a vector.Direction cosines and direction ratios of a vector. Types of vectors (equal, unit, zero, parallel and collinear vectors), position vector of a point, negative of a vector, components of a vector, addition of vectors, multiplication of a vector by a scalar, position vector of a point dividing a line segment in a given ratio. Definition, Geometrical Interpretation, properties and application of scalar (dot) product of vectors, vector (cross) product of vectors, scalar triple product of vectors.