Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    5
    ReputationRep:
    Given instead that B has speed 8 m s–1 and moves in the direction of the vector (3i + 4j),

    (d) find the distance of B from P when t = 7 s.

    *I understand how to do this question but there is one thing which I want to know"

    In the mark scheme is changes the speed into 8/5 I undestand they did that to get V to insert into an equation but how do you change the speed of 8 into a velocity of 8/5?

    Thanks.
    Offline

    16
    ReputationRep:
    (Original post by A*GLORYHUNTER)
    Given instead that B has speed 8 m s–1 and moves in the direction of the vector (3i + 4j),

    (d) find the distance of B from P when t = 7 s.

    *I understand how to do this question but there is one thing which I want to know"

    In the mark scheme is changes the speed into 8/5 I undestand they did that to get V to insert into an equation but how do you change the speed of 8 into a velocity of 8/5?

    Thanks.
    We use a unit vector. So we do the vector divided by its magnitude. Then we multiply this by 8. Hence (3i - 4j )/ 5 * 8 = 24/5i - 32/5j
    • Thread Starter
    Offline

    5
    ReputationRep:
    (Original post by Someboady)
    We use a unit vector. So we do the vector divided by its magnitude. Then we multiply this by 8. Hence (3i - 4j )/ 5 * 8 = 24/5i - 32/5j
    Oh I see how did you get 5 as the magnitude
    Offline

    16
    ReputationRep:
    (Original post by A*GLORYHUNTER)
    Oh I see how did you get 5 as the magnitude
    3^2 + 4^2 = 25. Square root 25 = 5.
    • Thread Starter
    Offline

    5
    ReputationRep:
    (Original post by Someboady)
    3^2 + 4^2 = 25. Square root 25 = 5.
    Thank you so much!
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Brussels sprouts
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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