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Need help on calculating the distance between position vectors watch

    • Thread Starter

    (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

    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

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

    Ignore the thread, realised the silly mistake I did
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