Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    4
    ReputationRep:
    A bird has a speed in still air of 20 ms-1. It is pointed in the direction of the bearing 130 degrees, but there is a wind blowing at a speed of 10 m/s from the south west.

    Take unit vectors i to point east and j to point north.

    a) Express velocity of the bird relative to the air and the velocity w of the wind in compnent form, giving numerical values in ms-1 and the direction as a bearing to the nearest degree.

    b) express resultant velocity v of the bird in componenet form , giving the numerical values in ms-1 to 2 d.p

    c) hence find the magnitude and directon of the resultant velocity v of the bird, giving the magnitiude in ms-1 to 2 d.p and the direction as a bearing to the nearest degree.



    I'm completely stuck. I do not understand it at all. Ive tried drawing a right handed triangle, and I've only managed to get wind velocity using 10cos45 i + 10 sin45 j...and I don't even know if thats right. I really need to be talked through this...
    • Community Assistant
    Online

    20
    ReputationRep:
    Community Assistant
    (Original post by aliceinwonder123)
    ...
    Take the bird's velocity. We know that it is going at a speed of 20m/s in the direction of 130 degrees. So, draw your i and j axes. Measure 130 degrees from the +ve j axis clockwise, put a point down, and connect it to the origin. Draw the arrow to indicate direction of travel. Notice that it it moving in the +ve i direction but -ve j direction. So, then note that the angle between this vector and the +ve i axis is 40 degrees. Hence, the vector is ... ?
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by RDKGames)
    Take the bird's velocity. We know that it is going at a speed of 20m/s in the direction of 130 degrees. So, draw your i and j axes. Measure 130 degrees from the +ve j axis clockwise, put a point down, and connect it to the origin. Draw the arrow to indicate direction of travel. Notice that it it moving in the +ve i direction but -ve j direction. So, then note that the angle between this vector and the +ve i axis is 40 degrees. Hence, the vector is ... ?


    is....320 degrees?

    So I shouldnt have drawn a right handed triangle?

    I dont know how to visualise the vectors. To be quite honest, I didnt understand how a direction of 130 degrees would look until you explain it in words.
    • Community Assistant
    Online

    20
    ReputationRep:
    Community Assistant
    (Original post by aliceinwonder123)
    is....320 degrees
    Not quite what I was going for...

    The vector for bird's velocity is thus 20cos(40)i - 20sin(40)j

    Diagram:
    Spoiler:
    Show





    Now just repeat the same approach to obtain the velocity vector of the wind.

    (Original post by aliceinwonder123)
    I dont know how to visualise the vectors. To be quite honest, I didnt understand how a direction of 130 degrees would look until you explain it in words.
    You should be OK with this because this is a GCSE topic that you would've done. If you're not, then I recommend you talk to your teacher so they can help you with the visualisation part and understand the bearing stuff.
    • Thread Starter
    Offline

    4
    ReputationRep:
    (Original post by RDKGames)
    Not quite what I was going for...

    The vector for bird's velocity is thus 20cos(40)i - 20sin(40)j

    Diagram:
    Spoiler:
    Show







    Now just repeat the same approach to obtain the velocity vector of the wind.



    You should be OK with this because this is a GCSE topic that you would've done. If you're not, then I recommend you talk to your teacher so they can help you with the visualisation part and understand the bearing stuff.
    wow, thanks for the diagram. I wasnt getting anything near that. I have so many questions, but I guess i'll come back once I've learnt more.

    Been 8 years since I've studied GCSE, and I really can't remember vectors.

    One question,

    will the wind velocity be a seperate diagram, or drawn on the same one?
    • Community Assistant
    Online

    20
    ReputationRep:
    Community Assistant
    (Original post by aliceinwonder123)
    will the wind velocity be a seperate diagram, or drawn on the same one?
    Doesn't matter, though part (b) would require you to draw both vectors on the same diagram for visual aid.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: February 6, 2018
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.