[blueray]

Can you help me on how to answer this please

I don't know how to do part 1

I can work out the distance for part ii) But not the time
Therefore I can't do part iii) either

And i'm also a bit confused as to what the instructions are saying?

Eg a ship is moving on a bearing of 170 at 21 knots ( a bearing from where??)

Thanks!

(question bellow)

[CharlieBoardman]

The ship is at point A, and is moving at a bearing of 170degrees from that point (towards C). So we know that angle NAC(the N on the RHS) is 170. You can also figure out angle LAN(the N on the RHS), with a simple geometry rule. When you know both those angles, you can show angle LAC=50, as angles in a circle=360.

[blueray]

(Original post by CharlieBoardman)
The ship is at point A, and is moving at a bearing of 170degrees from that point (towards C). So we know that angle NAC(the N on the RHS) is 170. You can also figure out angle LAN(the N on the RHS), with a simple geometry rule. When you know both those angles, you can show angle LAC=50, as angles in a circle=360.

Yeah but the answer just says

Angle LAC = 40 + 10 = 50

nothing to do with angles in a circle

Ps is this what you are trying to say??

[CharlieBoardman]

(Original post by blueray)
Yeah but the answer just says

Angle LAC = 40 + 10 = 50

nothing to do with angles in a circle

Ps is this what you are trying to say??

Yes, that is the way which I meant. The mark scheme has just found the angle a different way, that's all! They have used the fact that you have a 'Z' angle, and added the 10degrees left over from your 170degrees. Either method, you'll still get the marks

To find the time for part 2, use the fact that t=d/s

[blueray]

(Original post by CharlieBoardman)
Yes, that is the way which I meant. The mark scheme has just found the angle a different way, that's all! They have used the fact that you have a 'Z' angle, and added the 10degrees left over from your 170degrees. Either method, you'll still get the marks

To find the time for part 2, use the fact that t=d/s

Surely that would make it 40 not 50 then? And why add 10 if it's not a straight line

[CharlieBoardman]

(Original post by blueray)
Surely that would make it 40 not 50 then? And why add 10 if it's not a straight line

Part of the angle is 40, but the remainder of the angle is 10 - as angles on a straight line = 180.
If you extend the N line downwards, it might make it clearer.

[raheem94]

(Original post by blueray)
Surely that would make it 40 not 50 then? And why add 10 if it's not a straight line

See the below diagram:

[blueray]

(Original post by CharlieBoardman)
Part of the angle is 40, but the remainder of the angle is 10 - as angles on a straight line = 180.
If you extend the N line downwards, it might make it clearer.

(Original post by raheem94)
See the below diagram:

Haha cheers thanks! I was wondering why that was!

[CharlieBoardman]

(Original post by blueray)
Haha cheers thanks! I was wondering why that was!

(Original post by raheem94)
See the below diagram:

I wish I could upload photos onto TSR from my iPad! It would make explanations so much easier sometimes.

[blueray]

(Original post by CharlieBoardman)
I wish I could upload photos onto TSR from my iPad! It would make explanations so much easier sometimes.

You can upload it to image shack then upload it

[raheem94]

(Original post by CharlieBoardman)
I wish I could upload photos onto TSR from my iPad! It would make explanations so much easier sometimes.

From iPad it will be even easier, you will be able to draw these diagrams by hand, right?

Then upload on imageshack(like i do) and give the link.

[CharlieBoardman]

(Original post by blueray)
You can upload it to image shack then upload it

(Original post by raheem94)
From iPad it will be even easier, you will be able to draw these diagrams by hand, right?

Then upload on imageshack(like i do) and give the link.

Image shack? Why haven't I heard of this?! I swear I'm completely oblivious to half of the things on the Internet. -.- I'm going to have to check this out, because I imagine it will be easy to draw on an iPad!

[raheem94]

(Original post by CharlieBoardman)
Image shack? Why haven't I heard of this?! I swear I'm completely oblivious to half of the things on the Internet. -.- I'm going to have to check this out, because I imagine it will be easy to draw on an iPad!

Image shack is just a image uploading site, like photobucket.

I just draw the diagrams, if it requires less work then i use paint, if more work then i use photoshop, then just upload the image on imageshack, and insert the link on TSR.

[CharlieBoardman]

(Original post by raheem94)
Image shack is just a image uploading site, like photobucket.

I just draw the diagrams, if it requires less work then i use paint, if more work then i use photoshop, then just upload the image on imageshack, and insert the link on TSR.

Found it, and figured it out! Cheers raheem!

[blueray]

(Original post by raheem94)
x.

(Original post by CharlieBoardman)
x

I have done part 2 No problems

How do I do part iii?

Thanks!

[Math12345]

(Original post by blueray)
I have done part 2 No problems

How do I do part iii?

Thanks!

Lets call the place where the ship is 110 degrees from the lighthouse 'D'.

Say D is where the arrow is pointing down from C.

Draw the triangle out - LDC.

You should know CLD = 30 degrees and CDL = 60 degrees

Use the sine rule to find trinagle ALD.

Then the time taken from A to C is your answer divided by 21 - convert it into minutes.

You should know how to work out the time when the ship is at D.

[blueray]

(Original post by Math12345)
Lets call the place where the ship is 110 degrees from the lighthouse 'D'.

Say D is where the arrow is pointing down from C.

Draw the triangle out - LDC.

You should know CLD = 30 degrees and CDL = 60 degrees

Use the sine rule to find trinagle ALD.

Then the time taken from A to C is your answer divided by 21 - convert it into minutes.

You should know how to work out the time when the ship is at D.

How am I meant to know that?

[Math12345]

(Original post by blueray)
How am I meant to know that?

You know the bearing is 110. Just take away 40 and 40 from it to leave 30. The other angle is 180-90-30=60

[blueray]

(Original post by Math12345)
You know the bearing is 110. Just take away 40 and 40 from it to leave 30. The other angle is 180-90-30=60

Why? Why would do that?

[Math12345]

(Original post by blueray)
Why? Why would do that?

Because you have two triangles where the left angles are 40.