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    • Thread Starter


    I am stuck with one question below.. I've done parts a-c and having a bit of problem with d. I hope you can help me this as it seems I cannot find the right answer (which is 10.5) . Thanks..

    [In this question, the unit vectors i and j are due east and due north respectively.]
    A particle P is moving with constant velocity (–5i + 8j) m s–1. Find

    (a) the speed of P,
    (b) the direction of motion of P, giving your answer as a bearing.

    At time t = 0, P is at the point A with position vector (7i – 10j) m relative to a fixed origin O. When t = 3 s, the velocity of P changes and it moves with velocity (ui + vj) m s–1, where u and v are constants. After a further 4 s, it passes through O and continues to move with velocity (ui + vj) m s–1.

    (c) Find the values of u and v.
    (d) Find the total time taken for P to move from A to a position which is due south of A.

    presumably you get u = +2, v= -3.5

    You then need to be at a position where the I is the same as at A, ie I = +7

    So the time to do that will be 3 for the first velocity, 4 seconds to get to the origin and then whatever it takes to get to +7I.
    • Thread Starter

    oh.. easy easy easy!... i got 3.5s for origin to 7i but didn't realise that i have to add 3s and 4s.. thanks!
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Updated: July 16, 2009

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