Two people are standing 10 m apart (horizontally) when they start walking away from each other. The first person walks north at a rate of 1.5and the second person walks south at a rate of 1.8. What is the rate of change of the distance between the two people 10 seconds after they started walking?

Answer 1

after t seconds, the distance z is
z^2 = 10^2 + (1.5t+1.8t)^2 = 100 + 10.89t^2
2z dz/dt = 21.78t
so now find z when t=10, and then solve for dz/dt
2*34.48 dz/dt = 217.8
dz/dt = 3.158 m/s