Question

Train A crosses train B, which is stationary, in 90 seconds. After a few minutes, train B travels at a uniform speed and crosses train C
running at twice the speed in the opposite direction, in 30 seconds. If the trains are of equal length, what is the ratio of their speeds?​

Answer 1

Given : Train A crosses train B, which is stationary, in 90 seconds.

Train B travels at a uniform speed and crosses train C  running at twice the speed in the opposite direction, in 30 seconds.

the trains are of equal length,

To Find : what is the ratio of their speeds?​

Solution:

Let say length of Each train = L m

Train A crosses train B, which is stationary, in 90 seconds.

Distance covered by Train A = 2L  m

Speed of Train A = 2L/90    = L/45  m/s

train B travels at a uniform speed and crosses train C

running at twice the speed in the opposite direction, in 30 seconds.

Speed of train B  =  B    Speed of Train C  = 2B

Relative speed =  B + 2B  = 3B

Distance Covered  = 2 L  m

Time 30 Sec

=> 3B  = 2L/30

=> B = L/45

Speed of Train A =  L/45  m/s

Speed of Train  B  =   L/45  m/s

Speed of Train  C =   2L/45  m/s

Ratio of Speeds of Train A , B &  C are = 1  : 1 : 2

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