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Relative Velocity Question watch

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    QUESTION:
    Two particles A and B have the position vectors rA = ti -cos(2t)j-3k and rB = sin(t)i +(3+2t)j +7k respectively.

    Find all the times t such that a stationary observer would see:

    a) A moving in a direction perpendicular to the motion of B
    b) A accelerating in the direction B is travelling
    c) A moving directly towards B

    Any suggestions about finding the answers? I've differentiated both position vectors to find velocity and acceleration.
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    (Original post by 123student456)
    QUESTION:
    Two particles A and B have the position vectors rA = ti -cos(2t)j-3k and rB = sin(t)i +(3+2t)j +7k respectively.

    Find all the times t such that a stationary observer would see:

    a) A moving in a direction perpendicular to the motion of B
    b) A accelerating in the direction B is travelling
    c) A moving directly towards B

    Any suggestions about finding the answers? I've differentiated both position vectors to find velocity and acceleration.
    For a) you need to solve \vec{v}_A \cdot \vec{v}_B = 0 since that is the condition for the velocity vectors to be perpendicular.

    Can you find similar conditions for b) and c) ?
 
 
 
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