# Homework Help: Help with a vector problem

1. Sep 18, 2004

### motionman04

Find the horizontal and vertical components of the d = 140 m displacement of a superhero who flies from the top of a tall building following the path shown in Fig. P3.18 where = 35.0°.

The picture is here http://www.webassign.net/pse/p3-20alt.gif

Not sure of exactly where to start.

2. Sep 18, 2004

### faust9

Start by drawing a triangle and writing what you know on it.

3. Sep 18, 2004

### motionman04

well i was able to get the vertical by 140 cos 35, but as I tried 140 sin 35, the answer turned out to be wrong.

4. Sep 18, 2004

### Sirus

Remember your trigonometry: what does cos 35 equal in this triangle? What does sin 35 equal?

5. Sep 18, 2004

### rocky811

I have a question....do you know what the right answer is...because i think i figured it out......ALSO, I don't know if I'm looking at the problem right...but to me the VERTICAL component (Y) looks to me to be opposite of the angle, which would make the y component 140 sin 35...and the x component is adjacent to the angle, which is 140cos 35

6. Sep 18, 2004

### Sirus

That is what I was getting at, hoping motionman would figure it out on his own.

7. Sep 18, 2004

### motionman04

Well I know that sin = opposite over hypotenuse, and cos = adjacent over hypotenuse, I tried 140 sin 35 but apparently thats wrong

8. Sep 18, 2004

### Sirus

The vertical (y) component should be 140 sin 35, the horizontal (x) component should be 140 cos 35. Make sure your calculator is in degree mode.

9. Sep 18, 2004

### motionman04

yep, its in degree mode, and I get an answer of 80.3007 m, however, its wrong for some reason

10. Sep 19, 2004

### CinderBlockFist

140sin35 = 80.3007, so u are right, what does the answer say in the book?

11. Sep 19, 2004

### motionman04

Well its a problem is on webassign.com, and each time I put in that number, it says it is incorrect

12. Sep 19, 2004

### CinderBlockFist

maybe put negative -80.3007, since it is negative according to the x and y axis on how the diagram is labeled. Other than that, the only thing i can think of is check your significant digits, and how accurate webassign.com wants ur answeres to be.

13. Sep 19, 2004

### motionman04

Yep, that did the trick, thanks for that one cinderblock

14. Sep 19, 2004

### CinderBlockFist

No problem bro

15. Sep 19, 2004

### motionman04

I've got another problem thats been stumping me, it goes like this:

Instructions for finding a buried treasure include the following: Go 77.0 paces at 245°, turn to 130° and walk 110 paces, then travel 100 paces at 162°. The angles are measured counterclockwise from an axis pointing to the east, the +x direction. Determine the resultant displacement from the starting point.

Now, I've found the x, y components for all three vectors, by doing

77 cos/sin 245, 110 cos/sin 130, 100 cos/sin 162, and after finding the resultant vector for the x, it turned out to be wrong.

16. Sep 19, 2004

### Pyrrhus

I hate this Web applets, if you put too many numbers it will say wrong...

try putting -80.30

Last edited: Sep 19, 2004
17. Sep 19, 2004

### Pyrrhus

Use the components!!

Sum all the X components and the Y components, and you will have the displacement in X component and Y component.

Well other than that, let me try

$$\vec{R} = (R_{x}i + R{y}j) m$$

$$R_{x} = 77cos(245) + 110cos(130) + 100cos(162)$$

$$R_{y} = 77sin(245) + 110sin(130) + 100sin(162)$$

$$\vec{R} = (-198.35i + 45.38j) m$$

$$|\vec{R}| = \sqrt{(-198.35)^2 + (45.38)^2} = 203.47 m$$

$$\theta_{R} = 167.11^o$$ Counter-Clockwise.

Last edited: Sep 19, 2004
18. Sep 19, 2004

### motionman04

Yeah, I did, I got the resultant vector for the x components and used that as the displacement vector from the starting point

19. Sep 19, 2004

### Pyrrhus

i don't think that's what is asking. It's asking for the Resultant Vector.

20. Sep 19, 2004

### motionman04

haha no luck with the 221 or 315 degrees,