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    • Thread Starter

    Hi there,
    I am new to TSR so be kind! :p:

    A quick question about M1 really:

    A Jet Ski is at the origin and is travelling due north at 5ms-1 when it begins to accelerate uniformly. After accelerating for 40 seconds, it is travelling due east at 4ms-1.

    c) The Jet Ski is travelling southeast t seconds after it leaves the origin.
    i) find t.
    ii) find the velocity of the Jet Ski at this time.

    I just get confused when the particle is moving southeast, or northeast etc. I can work it out when it is travelling North or East as i=0 or j=0; I am not too sure what to do when it is southeast etc. though.

    Any help will be very much appriciated, thank you in advance!

    Southeast means +ve i and -ve j components. Also the magnitude of the two components are equal, so you're looking at solving an equation of the form y=-x where x is the i component and y is the j component.

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    • Thread Starter

    Yeah I get that now!
    Thanks very much

    We need to look at the components of acceleration seperetly.

    For the vertical direction.

    We use v = u + at to see that:

    0 = 5ms^-1 + (a)(40s)
    then a = -0.125ms^2

    For the horizontol direction

    4ms^-1 = 0 + (a)(40s)
    then a = 0.1ms^-2

    For the jetski to be travelling southeast, the vertical and horizontal componenets of velocity must be equal in magnitude.

    Then 5ms^-1 + (-0.125ms^-2)(t) = 0 + (0.1ms^-2)(t)

    Here, t = 22.2s

    So if we add the initial 40s of travel our answer is 62.2s

    Hope this helps.
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Updated: January 14, 2010

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