Two people depart from the same spot.One traveling North at at 5 ft per second and one traveling East at 1 ft per second.How fast are they separating from each other after 5 seconds?
the distance z at time t is
z^2 = (5t)^2 + (1t)^2 = 26t^2
z = √26 t
so z is always increasing at √26 ft/s