# What is the speed of an object that travels from ( -4,6,2)  to ( -3, 9,-6 )  over 3 s?

The displacement from one point to the other is $d = \sqrt{{\left({x}_{2} - {x}_{1}\right)}^{2} + {\left({y}_{2} - {y}_{1}\right)}^{2} + {\left({z}_{2} - {z}_{1}\right)}^{2}} = \sqrt{{\left(- 3 - \left(- 9\right)\right)}^{2} + {\left(9 - 6\right)}^{2} + {\left(- 6 - 2\right)}^{2}}$
$= \sqrt{36 + 9 + 64} = \sqrt{109} \approx 10.44$ units.
Speed = distance/time = $\frac{10.44}{3} = 3.5$ $m {s}^{-} 1$.