Question

Train A, travelling at 84 kmph, overtook train B, traveling in the same direction, in 10 seconds. If train B had been traveling at twice of its original speed, then train A would have taken 22.5 seconds to overtake it. Find the length of train B, given that it is half the length of train A.

Answer 1

Distance train A has to travel to cross train B = 2L + L = 3L
(L is the length of Train B and 2L is the length of train A)
84 Kmph = 70/3 (m/s)
Relative speed between between the trains = 70/3 - Vb
(Velocity of Train B)
(3L/(70/3 - Vb)) = 10
Vb = 70/3 - (3/10)L -------- 1
If train B is going @ 2×Vb then
Vb = 35/3 - L/15 --------- 2
Equating 1 and 2
L = 50m = Length of Train B.