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24.<br />

25. a. 0a !<br />

b. 0a ! 0 2 0b ! a<br />

2<br />

0 2<br />

c. 4 0a ! 0b ! 0<br />

0 2<br />

0 2<br />

26. Case 1 If and are collinear, then<br />

2b ! is also collinear with both<br />

and . But is perpendicular to and<br />

c ! c ! 4c ! b ! 9 0b ! c ! 0 2<br />

, so a ! a !<br />

is perpendicular to .<br />

Case 2 If b ! and c ! 2b ! b ! b !<br />

4c !<br />

are not collinear,<br />

then by spanning sets, and span a<br />

plane in R 3 , and is in that<br />

plane. If a ! 2b ! b !<br />

4c ! c !<br />

is perpendicular to b !<br />

and c ! ,<br />

then it is perpendicular to the plane<br />

and all vectors in the plane. So, is<br />

perpendicular to 2b ! 4c ! a !<br />

.<br />

Chapter 6 Test, p. 348<br />

1. Let P be the tail of and let Q be<br />

the head of The vector sums<br />

3a ! 1b ! c ! a !<br />

c ! .<br />

24 and 31a ! b ! 2 c ! 4 can<br />

be depicted as in the diagram below,<br />

using the triangle law of addition.<br />

We see that<br />

1a ! b ! PQ !<br />

2 c ! a ! 1b ! c ! 2 <br />

. This is the associative<br />

property for vector addition.<br />

P<br />

b<br />

a<br />

(a + b)<br />

(b + c)<br />

c<br />

PQ= (a + b) + c = a + (b + c)<br />

2. a. (8, 4, 8)<br />

b. 12<br />

c. a 2 3 , 1 3 , 2 3 b<br />

3. 19<br />

4. a. x ! 2b ! 3a ! , y ! 3b ! 5a !<br />

b. a , ,<br />

5. a. a ! 1<br />

and b ! b 5 c 11<br />

span R 2 , because any<br />

vector (x, y) in R 2 can be written as<br />

a linear combination of a ! and b ! .<br />

These two vectors are not multiples<br />

of each other.<br />

b. p 2,<br />

q 3<br />

6. a. 11, 12, 292 213, 1, 42 <br />

711,<br />

b. r ! 2,32<br />

cannot be written as a linear<br />

combination of and In other<br />

words, r ! p ! q ! .<br />

does not lie in the plane<br />

determined by p ! and q ! .<br />

7. 13, u 3.61; 73.9° relative to x<br />

b<br />

Q<br />

8.<br />

DE !<br />

DE ! CE !<br />

b ! <br />

a ! CD !<br />

Also,<br />

BA ! CA ! CB !<br />

BA ! 2b ! 2a !<br />

Thus,<br />

DE ! 1 2 BA!<br />

Chapter 7<br />

Review of Prerequisite Skills,<br />

p. 350<br />

1. v 806 km><br />

h N 7.1° E<br />

2. 15.93 units W 32.2° N<br />

3.<br />

z<br />

x<br />

4. a.<br />

b.<br />

c.<br />

13, 2, 72; l 7.87<br />

19, 3, 142; l 16.91<br />

11, 1, 02; l 1.41<br />

d. 12, 0, 92; l 9.22<br />

c. (0, y, z)<br />

6. a. i ! <br />

b. 6i ! 7j !<br />

<br />

c. 8i ! 2j !<br />

d. 4i ! <br />

7. a. i ! 6j ! 11j ! <br />

<br />

b. 5i ! 3j ! <br />

<br />

c. 12i ! j ! k ! 8k ! 3k !<br />

<br />

j ! k !<br />

2k !<br />

5. a. (x, y, 0)<br />

b. (x, 0,z)<br />

Section 7.1, pp. 362–364<br />

1. a. 10 N is a melon, 50 N is a chair,<br />

100 N is a computer<br />

b. Answers will vary.<br />

2. a.<br />

10 N<br />

30 N<br />

C(–2, 0, 1)<br />

B(–3, 2, 0)<br />

y<br />

A(0, 1, 0)<br />

D(0, 2, –3)<br />

20 N<br />

b. 180°<br />

3. a line along the same direction<br />

4. For three forces to be in equilibrium,<br />

they must form a triangle, which is a<br />

planar figure.<br />

5. a. The resultant is 13 N at an angle of<br />

N 22.6° W. The equilibrant is 13 N<br />

at an angle of S 22.6° W.<br />

b. The resultant is 15 N at an angle of<br />

S 36.9° W. The equilibrant is 15 N at<br />

N 36.9° E.<br />

6. a. yes b. yes c. no d. yes<br />

7. Arms 90 cm apart will yield a resultant<br />

with a smaller magnitude than at<br />

30 cm apart. A resultant with a smaller<br />

magnitude means less force to counter<br />

your weight, hence a harder chin-up.<br />

8. The resultant would be 12.17 N at<br />

34.7° from the 6 N force toward the<br />

8 N force. The equilibrant would be<br />

12.17 N at 145.3° from the 6 N force<br />

away from the 8 N force.<br />

9. 9.66 N 15° from given force, 2.95 N<br />

perpendicular to 9.66 N force<br />

10. 49 N directed up the ramp<br />

11. a.<br />

7 N<br />

b. 60°<br />

12. approximately 7.1 N 45° south of east<br />

13. a. 7<br />

b. The angle between f 1 and the<br />

resultant is The angle between<br />

f ! 16.3°.<br />

1 and the equilibrant is 163.7° .<br />

14. a.<br />

1 N<br />

60°<br />

8 N<br />

60°<br />

1 N<br />

13 N<br />

1 N<br />

60°<br />

For these three equal forces to be in<br />

equilibrium, they must form an<br />

equilateral triangle. Since the<br />

resultant will lie along one of these<br />

lines, and since all angles of an<br />

equilateral triangle are 60°, the<br />

resultant will be at a 60° angle with<br />

the other two vectors.<br />

670 Answers<br />

NEL

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