How fast must the train travel the next 80 km so as to average 60 km h-1 for the entire trip if it traveled a 120 km track for the first 40 km at a uniform speed of 40 km h-1?

Answer 1

distance = speed x time

First 40 km = 40 t1 and thus t1 = 1 hour

Total distance = 120km = ave speed x t total= 60 this t total= 2 hours

second part = distance = 80 = new speed x (t total - t1) = new speed x 1 hr

new speed = 80 km per hour