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    aroumieh's Avatar
    aroumieh Posts: 1, Reputation: 1
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    #1

    Sep 12, 2012, 08:52 PM
    Kinematics
    The position vector of a particle a P at time t is R=(1-t^2)i+(3t-5t^2)j. Find the time at which P is directly moving towards the origin.
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Sep 13, 2012, 06:14 AM
    Hint: determine the expression for the velocity vector in terms of I and j, then set the slope of the velocity vector = slope of the position vector and solve for 't'. Then verify for which values of 't' the velocity vector is pointed toward the origin (as opposed to away from it). Post back with what you get and we'll check it for you.
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