[PDF] VECTOR ALGEBRA operations on vectors and their

View - Download VECTOR ALGEBRA

Previous PDF

Next PDF

MATHEMATICS

In most sciences one generation tears down what another has built and wh at one has established another undoes. In Mathematics alone each generation builds a new story to the old structure. - HERMAN HANKEL ❖

10.1 Introduction

In our day to day life, we come across many queries such as - What is your height? How should a football player hit the ball to give a pass to another player of his team? Observe that a possible answer to the first query may be 1.6 meters, a quantity that involves only one value (magnitude) which is a real number. Such quantities are called scalars. However, an answer to the second query is a quantity (called force) which involves muscular strength (magnitude) and direction (in which another player is positioned). Such quantities are called vectors. In mathematics, physics and engineering, we frequently come across with both types of quantities, namely, scalar quantities such as length, mass, time, distance, speed, area, volume, temperature, work, money, voltage, density, resistance etc. and vector quantities like displacement, velocity, acceleration, force, weight, momentum, electric field intensity etc. In this chapter, we will study some of the basic concepts about vectors, various operations on vectors, and their algebraic and geometric properties. The se two type of properties, when considered together give a full realisation to the conc ept of vectors, and lead to their vital applicability in various areas as mentioned abov e.

10.2 Some Basic Concepts

Let ' l' be any straight line in plane or three dimensional space. This line can be given two directions by means of arrowheads. A line with one of these directions prescribed is called a directed line (Fig 10.1 (i), (ii)).Chapter 10

VECTOR ALGEBRAW.R. Hamilton

(1805-1865)

VECTOR ALGEBRA

Now observe that if we restrict the line l to the line segment AB, then a magnitude is prescribed on the line l with one of the two directions, so that we obtain a directed line segment (Fig 10.1(iii)). Thus, a directed line segment has magnitude as wel l as direction.

Definition 1

A quantity that has magnitude as well as direction is called a vector. Notice that a directed line segment is a vector (Fig 10.1(iii)), den oted as initial point, and the point B where it ends is called its terminal point. The distance between initial and terminal points of a vector is called the magnitude (or length) of the vector, denoted as |a. The arrow indicates the direction of the vector. Note Since the length is never negative, the notation | < 0 has no meaning.

Position Vector

From Class XI, recall the three dimensional right handed rectangular coord inate system (Fig 1

0.2(i)). Consider a point P in space, having coordinates (x, y, z) with respect to

the origin O(0, 0, 0). Then, the vector position vector of the point P with respect to O. Using distance formula (from Class XI), the magnitude of

2 22 x yz + +

Fig 10.1

MATHEMATICSAOP

90°

x,y,z C ??P( )x,y,z r

Direction Cosines

Consider the position vector x, y, z) as in Fig 10.3. The angles α, β, γ made by the vector x, y and z-axes respectively, are called its direction angles. The cosine values of these angles, i.e., cosα, cosβ and cosγ are called direction cosines of the vector l, m and n, respectively.

Fig 10.3

From Fig 10.3, one may note that the triangle OAP is right angled, and in it, we have cos a nd cosyz rrβ =γ = lr, mr,nr). The numbers lr, mr and nr, proportional to the direction cosines are called as direction ratios of vector a, b and c, respectively.Fig 10.2

VECTOR ALGEBRA

Note One may note that l2 + m2 + n2 = 1 but a2 + b2 + c2 ≠ 1, in general. 1

0.3 Types of Vectors

Zero Vector A vector whose initial and terminal points coincide, is called a zero vec tor (or null vector), and denoted as Unit Vector A vector whose magnitude is unity (i.e., 1 unit) is called a unit vecto r. The unit vector in the direction of a given vector ˆa Coinitial Vectors Two or more vectors having the same initial point are called coinitial vectors. Collinear Vectors Two or more vectors are said to be collinear if they are parallel to the same line, irrespective of their magnitudes and directions.

Equal Vectors Two vectors

Negative of a

Vector A vector whose magnitude is the same as that of a given vector (say, negative of the given vector.

For example, vector

Remark The vectors defined above are such that any of them may be subject to it s parallel displacement without changing its magnitude and direction. Such vectors are called free vectors. Throughout this chapter, we will be dealing with free vectors only.

Example 1 Represent graphically a displacement

of 40 km, 30° west of south.

Solution

The vector

Example 2 Classify the following measures as

scalars and vectors. (i)5 seconds (ii)1000 cm3Fig 10.4

MATHEMATICS

Fig 10.5

(iii)10 Newton(iv)30 km/hr(v)10 g/cm3 (vi)20 m/s towards north

Solution

Example 3

In Fig 10.5, which of the vectors are:

(i)Collinear(ii)Equal(iii)Coinitial

Solution

(i)Collinear vectors :

EXERCISE 10.1

1.Represent graphically a displacement of 40 km, 30° east of north.

2.Classify the following measures as scalars and vectors.

(i)10 kg(ii)2 meters north-west(iii)40° (iv)40 watt(v)10-19 coulomb(vi)20 m/s2

3.Classify the following as scalar and vector quantities.

(i)time period(ii)distance(iii)force (iv)velocity(v)work done

4.In Fig 10.6 (a square), identify the following vectors.

(i)Coinitial(ii)Equal (iii)Collinear but not equal

5.Answer the following as true or false.

(i)

Fig 10.6

VECTOR ALGEBRA

10.4 Addition of Vectors

A vector

triangle law of vector addition.

In general, if we have two vectors

Fig 10.7a

(i)(iii)AC a (ii) a AC B B a -b C 'Fig 10.8 For example, in Fig 10.8 (ii), we have shifted vector + , represented by the third side AC of the triangle ABC, gives us the sum (or resultant) of the vectors

MATHEMATICS

Now, construct a vector

difference of Now, consider a boat in a river going from one bank of the river to the oth er in a direction perpendicular to the flow of the river. Then, it is acted upon by two velocity vectors-one is the velocity imparted to the boat by its engine and ot her one is the velocity of the flow of river water. Under the simultaneous influence of these two velocities, the boat in actual starts travelling with a different velocity. To have a precise idea about the effective speed and direction (i.e., the resultant velocity) of the boat, we have the following law of vector addition.

If we have two vectors

parallelogram law of vector addition. Note From Fig 10.9, using the triangle law, one may note that

Properties of vector addition

Property 1 For any two vectors

Fig 10.9

VECTOR ALGEBRA

Proof Consider the parallelogram ABCD

(Fig 10.10). Let

Property 2 For any three vectors a bc

Proof Let the vectors

Fig 10.11

Then

Fig 10.10

MATHEMATICSaa12

a -2a a2and Remark The associative property of vector addition enables us to write the sum of three vectors a additive identity for the vector addition.

10.5 Multiplication of a Vector by a Scalar

L et λ a scalar. Then the product of the vector

λ, denoted as λ, is called the multiplication of vector λ. Note that, λis also a vector, collinear to the vector λ has the direction same (or

opposite) to that of vector λ is positive (or negative). Also, the magnitude of vector λ is |λ| times the magnitude of the vector

Fig 10.12

When

λ = -1, then λ= -

negative (or additive inverse) of vector and we always have

1=| |aλ ≠ 0 i.e.

VECTOR ALGEBRA

So, λ represents the unit vector in the direction of ˆa1 | |??aa?

Note For any scalar k,

0 =0. ? ?k10.5.1 Components of a vector

Let us take the points A(1, 0, 0), B(0, 1, 0) and C(0, 0, 1) on the x-axis, y-axis and z-axis, respectively. Then, clearly unit vectors along the axes OX, OY and OZ, respectively, and denoted by i jk x, y, z) as in Fig 10.14. Let P

1 be the foot of the perpendicular from P on the plane XOY.

We, thus, see that P1 P is parallel to z-axis. As

i jk x, y and z-axes, respectively, and by the definition of the coordinates of P, we haveFig 10.13

MATHEMATICS

Therefore, it follows that

component form. Here, x, y and z are called as the scalar components of xiy jzkvector components of x, y and z are also termed as rectangular components.

The length of any vector

r xiyj zk= ++

1 (Fig 10.14)

1P, we have

r xiyj zk= +

1 23 a ia ja k+

1 23 bib jb k+ +

1 12 23 3 a bi ab ja bk + ++ ++

1 12 23 3 a bi ab ja bk - +- +-

a

1 =b1, a2 = b2 and a3 = b3

(iv)the multiplication of vector λ is given by

1 23 a ia ja kλ +λ +λ

VECTOR ALGEBRA

The addition of vectors and the multiplication of a vector by a scalar t ogether give the following distributive laws:

Let k and m be any scalars. Then

(i)

Remarks

(i)One may observe that whatever be the value of λ, the vector λ is always collinear to the vector

λ such that

1 23 a ai aj ak = ++

1 23 bib jb k+ +1 23 a ia ja kλ ++ ?

1 23 ˆˆ ˆbib jb k =1 23 a ia ja kλ +λ +λ ?

1 1b a= λ,2 23 3,b ab a= λ= λ?

1 1 b a 32
2 3b b a a= =λ(ii)If

1 23 a ai aj ak = ++ a1, a2, a3 are also called direction ratios of

l, m, n are direction cosines of a vector, then lim jnk+ + i jk α +β +γ α, β and γ are the angles which the vector makes with x, y and z axes respectively. Example 4 Find the values of x, y and z so that the vectors Solution Note that two vectors are equal if and only if their corresponding compo nents are equal. Thus, the given vectors x = 2, y = 2, z = 1

MATHEMATICS

Example 5 Let

Solution

We have

Example 6

Find unit vector in the direction of vector Solution The unit vector in the direction of a vector

2 22 2 31 14 + +=

1ˆˆ ˆˆ(23 )14a ij k= ++ 2 31 ˆˆ ˆ

141 414i jk + +Example 7 Find a vector in the direction of vector

Solution

The unit vector in the direction of the given vector

11 2ˆ ˆˆ ˆ( 2) 55 5i ji j- =-

7a ?1 27

5 5i j

7 14ˆ ˆ

5 5i j-Example 8 Find the unit vector in the direction of the sum of the vectors,

Solution

The sum of the given vectors is

2 22 4 3( 2) 29+ +- =

VECTOR ALGEBRA

Thus, the required unit vector is14 32 ˆˆˆ ˆˆ ˆ(43 2)

29292 929i jk ij k= +- =+ -Example 9 Write the direction ratio's of the vector

Solution

Note that the direction ratio's a, b, c of a vector x, y and z of the vector. So, for the given vector, we have a = 1, b = 1 and c = -2. Further, if l, m and n are the direction cosines of the given vector, then

1 12 , ,-6 66

10.5.2 Vector joining two points

If P

1(x1, y1, z1) and P2(x2, y2, z2) are any two

points, then the vector joining P

1 and P2 is the

vector

1 and P2 with the origin

O, and applying triangle law, from the triangle

OP

1P2, we have

2 22 11 1 x iy jz kx iy jz k+ +- ++

2 12 12 1 x xi yy jz zk - +- +-

222

2 12 12 1( )( )( )x xy yz z- +- +- Fig 10.15

MATHEMATICS

Example 10 Find the vector joining the points P(2, 3, 0) and Q(- 1, - 2, -

4) directed

from P to Q.

Solution

Since the vector is to be directed from P to Q, clearly P is the initia l point and Q is the terminal point. So, the required vector joining P and Q is the vector i jk - -+ -- +- - i jk - -- 10.5.3 Section formula Let P and Q be two points represented by the position vectors

Case I When R divides PQ internally (Fig 10.16).

If R divides

m and n are positive scalars, we say that the point R divides m : n. Now from triangles ORQ and OPR, we have m : n is given byFig 10.16

VECTOR ALGEBRA

Case II When R divides PQ externally (Fig 10.17).

We leave it to the reader as an exercise to verify that the position vector of the point R which divides the line segment PQ externally in the ratio m : n PRi.e. QR = m n Remark If R is the midpoint of PQ , then m = n. And therefore, from Case I, the midpoint R of Example 11 Consider two points P and Q with position vectors

Solution

(i)The position vector of the point R dividing the join of P and Q internal ly in the ratio 2:1 is

Example 12

Show that the points

i jk ij ki jk - +- -- -

Solution

We have

i jk - +- ++ -- i jk = -- - i jk - +- ++ -+ i jk = -+ i jk - +- ++ + i jk = -+ +Fig 10.17

MATHEMATICS

Further, note that

EXERCISE 10.2

1.Compute the magnitude of the following vectors: i jk + + i jk - -1 11 ˆˆ ˆ

3 33 i jk + -2.Write two different vectors having same magnitude.

3.Write two different vectors having same direction.

4.Find the values of x and y so that the vectors

i jx iyj+ +

5.Find the scalar and vector components of the vector with initial point (

2, 1) and

terminal point (- 5, 7).

6.Find the sum of the vectors

i jk - + i jk - ++ c ij k= -

7.Find the unit vector in the direction of the vector

a ij k= ++

8.Find the unit vector in the direction of vector

9.For given vectors,

i jk - + i jk - +-

10.Find a vector in the direction of vector

i jk - +

11.Show that the vectors

i jk ij k- +- +-

12.Find the direction cosines of the vector

i jk + +

13.Find the direction cosines of the vector joining the points A(1, 2, -3) and

B (-1, -2, 1),

directed from A to B.

14.Show that the vector

i jk + +

15.Find the position vector of a point R which divides the line joining two

quotesdbs_dbs48.pdfusesText_48

[PDF] algebraic chess notation pdf

[PDF] algèbre 1 cours et 600 exercices corrigés pdf

[PDF] algebre 4

[PDF] algebre 5 sma pdf

[PDF] algebre exercices corrigés

[PDF] algebre exercices corrigés pdf

[PDF] alger avant 1962 photos

[PDF] alger bab el oued photos

[PDF] alger news

[PDF] algeria - wikipedia the free encyclopedia

[PDF] algeria wiki

[PDF] algeria wikipedia

[PDF] algerie 1 togo 0 2017

[PDF] algerie 1982

[PDF] algerie 1982 almond mache complet