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Lee-1127
May 1, 2009, 04:12 PM
Please help with this question
I tried working it out, but I couldn't get it at all

2 ships leave port. The first ship sails on a bearing of 270 degrees for 8 km while the second ship sails on a bearing of 200 degrees for 8 km. by drawing, find
(a) the distance between the ship
(b) the bearing of the first ship from the second
(c) the bearing of the second ship from the first

Mary99
May 1, 2009, 04:13 PM
Maybe try drawing out the problem?

Lee-1127
May 1, 2009, 04:20 PM
I did I couldn't get it

Mary99
May 1, 2009, 04:26 PM
Ahh is there a formula for it? I am trying to think back to Math class but I think we had a formula to figure out this problem.

Lee-1127
May 1, 2009, 04:27 PM
c2= a2+b2 - 2(a)(c)Cos x?

Lee-1127
May 1, 2009, 04:28 PM
or side a / sin a?
side b/ sin b?
side c/ sin c?

Mary99
May 1, 2009, 04:32 PM
This website might help you
Calculate distance and bearing between two Latitude/Longitude points using Haversine formula in JavaScript (http://www.movable-type.co.uk/scripts/latlong.html)

Mary99
May 1, 2009, 04:33 PM
Do you have the answers for a and b?

Lee-1127
May 1, 2009, 04:48 PM
No I don't :(

Lee-1127
May 1, 2009, 04:50 PM
It doesn't help
I need working!

Zazonker
May 1, 2009, 05:32 PM
Well, this can be solved mathematically, but the question as presented asks for a drawing. It is easiest to do with circular graph paper, but you can simulate that on regular paper if you are very careful in your measurements and use a large enough scale so that the thickness of your lead (might sound funny, but I don't mean it as a joke) doesn't degrade the accuracy of your answer.

If you use a scale something like 2 cm = 1 km you should be OK. Both ships start at the port, which would be the center of the circular graph. Draw one line 16 cm straight west (270 degrees). (or pick a different scale). Draw another line the same length at 200 degrees - which is SSW. The ends of the lines will give you the relative positions of the ships.
Measure the distance between the two positions. Apply your scale and you have the distance between the ships. For the bearing of ship 1 from ship 2, measure the angle offset from North.
With circular graph paper, you can use a parallel ruler lined up on the positions, slide to the center and read the bearing at the upper left part of the circle. On regular paper, there are a number of ways you can do it, but I think the easiest is to drop a perpendicular line from the course of ship 1 such that the line passes through ship 2's position. At the position of ship 2, measure the angle between this line and a line between the ship positions.

Subtract this from 360 degrees to get the bearing. Expect an answer somewhere around 350 degrees.

For the bearing of ship 2 from ship 1, either plot the logical opposite, or simply subtract 180 degrees

Lee-1127
May 1, 2009, 05:51 PM
And the distance?
I'm not getting that either

I don't know which angle to use in the cosine rule :(

Lee-1127
May 2, 2009, 02:59 PM
Which angle should I use in the cosine rule galactus?

galactus
May 2, 2009, 03:14 PM
The law of cosines is used when you have SAS.

You can see from the drawing, the angle needed is 70 degrees?

So, the distance between the ships is:

AB=\sqrt{8^{2}+8^{2}-2(8)(8)cos(70)}

Also, you can use the law of sines to find the other angles to aid in the other two parts of the problem.

Once you have the above solution, to find the angle at ship A use:

\frac{sin(A)}{8}=\frac{sin(70)}{AB}

then solve this for A to find that angle.

In other words, solved for angle A, it is A=sin^{-1}(\frac{8sin(70)}{AB})

One thing to note is that this is an isosceles triangle, therefore, angle B will be the same as angle A

Once you have those, parts b and c are easy.

Lee-1127
May 2, 2009, 03:16 PM
Are you sure galactus?

Lee-1127
May 2, 2009, 03:16 PM
How did u get 70 degrees in the first place man?

galactus
May 2, 2009, 03:24 PM
How did I get 70 degrees? Come on. What is 270-200?

Lee-1127
May 2, 2009, 03:30 PM
Oh Im sorry
I'm not smart like you... so yeah haha


What about the
The bearing of the first ship from the second and
The bearing of the second ship from the first

How do I do that?

Lee-1127
May 2, 2009, 06:28 PM
Galactus please help me out!

What about the
The bearing of the first ship from the second and
The bearing of the second ship from the first

How do I do that?

Unknown008
May 3, 2009, 01:53 AM
Look more carefully at Galactus' post


The law of cosines is used when you have SAS.

You can see from the drawing, the angle needed is 70 degrees?.

So, the distance between the ships is:

AB=\sqrt{8^2+8^2 - 2(8)(8)cos(70)}

Also, you can use the law of sines to find the other angles to aid in the other two parts of the problem.

Once you have the above solution, to find the angle at ship A use:

\frac{sinA}{8}=\frac{sin(70)}{AB}

then solve this for A to find that angle.

In other words, solved for angle A, it is A = sin^{-1}(\frac{8sin(70)}{AB})

One thing to note is that this is an isosceles triangle, therefore, angle B will be the same as angle A

Once you have those, parts b and c are easy.

Zazonker
May 3, 2009, 02:40 AM
I'm not even sure at this point that this is homework. I have a hard time believing that any school system in the world would give this type of problem to students who have no understanding of the underlying concepts. I think we have a child using multiple ids pretending he needs help just to waste peoples time.

Unknown008
May 3, 2009, 02:51 AM
Well, we can be sure of nothing... :( Nevertheless, I know that there are some teachers in my country who barely explain, or just state the formulae, then give work. Bad education system here... Well, I don't know for other countries.

Lee-1127
May 3, 2009, 10:43 AM
THis is hw :(
My teachers are always giving a lot of work
And she only goes through the easy ones
Which we already know
The hard ones she didn't even go through once

Unknown008
May 4, 2009, 06:03 AM
That's the tough part... Try to understand what is being done when we give you explications and example, and you'll able to do any difficult problem! ;)

ejos_mac
Apr 28, 2010, 08:50 AM
(a) the distance between the ship = 13.1km
(b) the bearing of the first ship from the second = 125 degrees
(c) the bearing of the second ship from the first = 305 degrees

ejos_mac
Apr 28, 2010, 08:51 AM
(a) the distance between the ship = 13.1km
(b) the bearing of the first ship from the second = 125 degrees
(c) the bearing of the second ship from the first = 305 degrees