Two trains of length 100 meter and 80 meter are running on parallel track . If they run in same direction they cross each other in 18 sec. and in opposite direction they cross each other in 9 sec . The speed of faster train is :
Answer & explanation
Correct answer: option 3
Total length = length of train 1 + length of train 2
= ( 100 + 80 )m = 180m
Speed of train 1 = x m/sec , speed of train 2 = y m/sec
When they move in same direction , relattive speed = ( x - y ) m/sec
Time = 18 sec
Relative speed ( x - y ) = \(\frac{180}{18}\) = 10 m/sec -------- ( 1 )
When they move in opposite direction , relative speed = ( x + y ) m/sec
Time = 9 sec
Relative speed ( x + y ) = \(\frac{180}{9}\) = 20 m/sec ------ ( 2 )
Add equation 1 and equation 2
2x = 30
x = 15 m/sec , y = 5 m/sec
Speed of faster train = 15 m/sec