x Turn on thread page Beta
 You are Here: Home >< Maths

1. Please explain part b, I understand part A but part B is confusing me too much. I've spent too long on it. Thank you.

A boat is travelling in water that is moving north-east at a speed of 2 m s1 . The velocity of the boat relative to the water is 5 m s1 due west.

(a) Show that the magnitude of the resultant velocity of the boat is 3.85 m s1 , correct to three significant figures. (4 marks)
(b) Find the bearing on which the boat is travelling, giving your answer to the nearest degree. (4 marks)
2. (Original post by Jas1947)
Please explain part b, I understand part A but part B is confusing me too much. I've spent too long on it. Thank you.
Have you? Post your workings then.
3. Attachment 553494553498
(Original post by Zacken)
Have you? Post your workings then.
Im sorry theyre sideways, i boxed the markscheme answer in pink
Attached Images

4. (Original post by Jas1947)

Im sorry theyre sideways, i boxed the markscheme answer in pink
Your problem stems from an incorrect diagram.

Here's the basics - resultant in green:

5. (Original post by ghostwalker)
Your problem stems from an incorrect diagram.

Here's the basics - resultant in green:

But im still struggling to get the correct answer, could some one please post their own working ?
6. (Original post by Jas1947)
But im still struggling to get the correct answer, could some one please post their own working ?

Your new problem is the sine rule. It does not distinguish between the angle x and the angle 180-x - they both have the same sin. This is something to be aware of if you use the sine rule.

In this case the angle is obtuse and you want 180 - 66.68.

Use of cosine rule would have avoided the ambiguity. Sine rule would be fine if you recognized it was an obtuse angle and acted accordingly.
7. (Original post by ghostwalker)

Your new problem is the sine rule. It does not distinguish between the angle x and the angle 180-x - they both have the same sin. This is something to be aware of if you use the sine rule.

In this case the angle is obtuse and you want 180 - 66.68.

Use of cosine rule would have avoided the ambiguity. Sine rule would be fine if you recognized it was an obtuse angle and acted accordingly.
Im sorry i dont understand
8. (Original post by Jas1947)
Im sorry i dont understand
Consider the shape of the sine curve. It increases from 0 to 90 and then decreases from 90 to 180,

If x is an angle between o and 90, then there is a corresponding angle 180-x, and they both have the same sine, sin(x) = sin(180-x). e.g. sin(30) = sin(150).

So, when you use the sine rule, and get sin(x) = 0.5 say, then x = 30 OR possibly x = 150 (that is 180-30). You don't know. You have to rely on the geometry of the situation to distinguish between the two values.

In this case the angle at A is actually obtuse, i.e greater than 90, so your angle is 180- "the angle you worked out".

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: June 20, 2016
Today on TSR

### Four things top students are doing

Over the Easter break

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams