Question

Two automobiles start from a point A at the same time. One travels west at 60km/hr and the other travels north 35 km/hr. how fast is the distance between them increasing 3hr later?

Answer 1

at time t hours, the distance d is

d^2 = (60t)^2 + (35t)^2
when t=3, then, d=208.39

Since

2d dd/dt = 7200t + 2450t = 9650t
at t=3,

dd/dt = 28950/(2*208.39) = 69.46 km/hr

Answer 2

very goog