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# Relative Velocity Question watch

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1. 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.
2. (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 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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Updated: October 22, 2015
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