Given that particles $P$ and $Q$ have velocities $a$i+$b$j and $x$i+$y$j, what is the condition that they are going in the same direction, and what is the condition that they are going in the opposite direction?
When are two particles moving in the same or opposite direction?
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classical-mechanics
1 Answers
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If $P$ has velocity $ai + bj$ then $Q$ is moving in the same (opposite) direction as $P$ if $xi + yj$ is a positive (negative) scalar multiple of $ai + bj$.