# Objects A and B are at the origin. If object A moves to (5, -1) and object B moves to (-7, 8) over 3 s, what is the relative velocity of object B from the perspective of object A? Assume that all units are denominated in meters.

This one seems tougher than it really is. The two objects start together at a separation of $0$ $m$, and end at a separation of $r = 15$ $m$, $3$ $s$ later. That means the relative velocity, $v = \frac{\Delta d}{\Delta t} = \frac{15}{3} = 5$ $m {s}^{-} 1$.
$r = \sqrt{{\left({x}_{2} - {x}_{1}\right)}^{2} + {\left({y}_{2} - {y}_{1}\right)}^{2}} = \sqrt{{\left(- 7 - 5\right)}^{2} + {\left(8 - \left(- 1\right)\right)}^{2}} = \sqrt{144 + 81} = 15$ $m$