Hey there! Sign in to join this conversationNew here? Join for free

Need help on calculating the distance between position vectors watch

    • Thread Starter
    Offline

    0
    ReputationRep:
    (vectors i and j are horizontal vectors in the direction due east and due north)
    Two boats A and B are moving with constant velocities. Boat A moves with velocity 9j km/h. Boat B moves with velocity (3i+5j)km/h.


    At noon, A is at the point O, and B is 10km due west of O. At time t hours after noon, the position vectors of A and B relative to O are a km and b km respectively.
    b)Find expressions for a and b in terms of t
    Ship a=6ti
    Ship b=3ti + (-10+5t)j


    c) find the time when B is due south of A
    1400


    At time t hours after noon, the distance between A and B is dkm. By finding the expression for ->AB
    d) show that d^2=25t^2-60t+100


    I'd appreciate some help on part d, I've tried using Pythagoras on the position vectors that I calculated in part b for ship A and B but didn't get the right answer (so the hypotenuse was the distance between AB)
    • Thread Starter
    Offline

    0
    ReputationRep:
    They've got the answer for d by taking away A from B, I don't understand why you'd take away :/
    • Thread Starter
    Offline

    0
    ReputationRep:
    Ignore the thread, realised the silly mistake I did
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
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.