A train travelling at 48 kmph completely crosses another train having half its length and travelling in opposite direction at 42 kmph, in 12 seconds. It also passes a railway platform in 45 seconds. The length of the platform is

A. 400 m
B. 450 m
C. 560 m
D. 600 m

• Length of the Ist train=2x m and the length of the other train be x m(1/2)
  The relative speed of the train(48+42)=90kmph or 25m/s
  Time taken to cross one another=12s
  Hence, 12=2x+x/25
  Solving, x=100m and 200m
  Now to determine the length of the platform
  45=100+length of the platform/speed of the Ist train
  45=100+L/240/18( 48kmph=240/118m/s)
  
  Solving, we get L=600M(option D)
• 13 years agoHelpfull: Yes(2) No(2)
• let the length of 1st train =x;
  then length of second train=x/2
  Speed of first train = 48kmph=(48*5/18=40/3msec)
  Speed of second train = 42 kmph
  
  because they are travelling in opposite dorection so their speed will be added hence
  relative spedd = 48+42=90kmph
  convert this in m/sec= 90*5/18=25m/sec.
  
  Now, by formula Speed= Distance/Time, we have(Distance=length of 1st train+length of second train)
  i.e. x+x/2
  25=x+x/2/12
  on solving, we get x=200(length of 1st train)
  x/2=100 (length of 2nd train)
  
  now, let the length of platform =y;
  then Same formula:- Speed =distance/time (with respect to first train)
  Speed= 48*5/18(for m/sec)=40/3m/sec.
  now, put in formula
  40/3=200+y/45
  
  y=400. Ans
  
  
  
  
• 10 years agoHelpfull: Yes(2) No(0)
• Let the length of the first train be 2d metres.
  
  Then, the length of the second train is ( ( metres.
  2
  
  Relative speed = (48 + 42) kmph = ( 90 x 5 ( m/sec = 25 m/sec.
  18
  
  Therefore [x + (x/2)] = 12 or 3x = 300 or x = 200.
  25 2
  
  Therefore Length of first train = 200 m.
  
  Let the length of platform be y metres.
  
  Speed of the first train = ( 48 x 5 ( m/sec = 40 m/sec.
  18 3
  
  Therefore (200 + y) x 3 = 45
  40
  
  => 600 + 3y = 1800
  
  => y = 400 m.
• 12 years agoHelpfull: Yes(1) No(0)
• correct one -Let the length of the first train be x metres.
  
  Then, the length of the second train is ( x ( metres.
  2
  
  Relative speed = (48 + 42) kmph = ( 90 x 5 ( m/sec = 25 m/sec.
  18
  
  Therefore [x + (x/2)] = 12 or 3x = 300 or x = 200.
  25 2
  
  Therefore Length of first train = 200 m.
  
  Let the length of platform be y metres.
  
  Speed of the first train = ( 48 x 5 ( m/sec = 40 m/sec.
  18 3
  
  Therefore (200 + y) x 3 = 45
  40
  
  => 600 + 3y = 1800
  
  => y = 400 m.
• 12 years agoHelpfull: Yes(0) No(0)