A freight train going in one direction takes 3 minutes to pass a crossing. A slower train of the same length on a parallel track in the other direction takes 4 minutes.
How long does it take these trains to pass each other?
Or in general if the two times are “a” and “b”, and the
train length is “L”, the two velocities are L/a and L/b.
Consider the frame
of reference to be one of the trains, as if one train was standing still. The desired time is the time it takes to go a
distance of 2L with a combined velocity of L/a + L/b
Time: 2ab / (a+b)
e.g. 2*3*4/7 = 3 3/7 as Steve Herman has posted.
Posted by Larry
on 2017-08-29 10:25:39