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Thread: relative velocity

  1. #1
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    relative velocity

    at midday a ship P has position -11i+j km relative to lighthouse o. At the same time the position of boat Q is 4i-13j km relative to o. The velocities of P and Q are 3i km/h and xj km/h respectively.
    if they are on a collision course what is the value of x

    so i got their relative displacements which is -15i-14j
    there relative velocities is 3i-xj
    if i get the slope of both these they should be the same if they are on a collision course .
    so -14/14=-x/3 x=2.8 the correct answer is 3. i do not see what I am doing wrong
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    Re: relative velocity

    $x_p=-11+3t$

    $y_p=1$

    $x_q=4$

    $y_q=-13+xt$

    setting the position components equal ...

    $-11+3t=4 \implies t=5$

    $1=-13+x\cdot 5 \implies x = 2.8$

    I agree with your solution. Maybe the given solution is rounded?
    Thanks from markosheehan
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  3. #3
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    Re: relative velocity

    yes the solution must be rounded.
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