Question

Two locomotives approach each other on parallel tracks. Each has a speed of 155km/h with respect to the ground. If they are initially 8.5 km apart. How long will it be before they reach each other

Answer 1

They're initially 8.5 km apart.

The open space between them is shrinking at the rate of 155 km/hr
from one end, and 155 km/hr from the other end, so the space is
closing at the rate of 310 km/hr.

The open space between them will shrink to zero in

(8,500 m) / (310,000 m/hr)

= 0.02742 of an hour

= 98.7 seconds