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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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228 Chapter 7 Vectors

F sin u

u

F

F cos u

Figure7.7

Aforce F can be resolved into two

perpendicular components.

5 sin 30°

30°

5

5 cos 30°

Figure7.8

The5Nforce can be resolved intotwo

perpendicular components.

x

Example7.1 Vectors p,q,r andsform the sidesofthe squareshown inFigure 7.9.Express

(a) pintermsof r

(b) sintermsof q

(c) diagonalBDintermsof qandr

Solution (a) The vector p has the same length as r but has the opposite direction. Therefore

p=−r.

(b) Vectorshasthesamelengthasqbuthastheoppositedirection.Therefores = −q.

(c) The head of BC → →

coincides with the tail of CD. Therefore, by the triangle law of

addition, the third sideoftriangle BCDrepresents the sum of → BCand → CD, thatis

BD = → BC + → CD

=q+r

7.2.4 Vectorsubtraction

Subtraction of one vector from another is performed by adding the corresponding negative

vector; thatis, ifweseeka −b, weforma + (−b).

Example7.2 ConsidertherectangleillustratedinFigure7.10withaandbasshown.Expressinterms

ofA,B, CorDthe vectors a −bandb −a.

B

p

q

C

r

a

B

C

A

s

Figure7.9

Thevectors p,q,r andsform the sides

ofasquare.

D

A

b

Figure7.10

Therectangle ABCD.

D

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