Two trains move in the same direction at speeds 50 kmph and 32 kmph respectively. A man in the slower train observes that 15 seconds elapse before the faster train completely passes by him. What is the length of faster train?
(a) 100m
(b) 75m
(c) 120m
(d) 50m

• Answer : (b) 75m
  
  This is a problem concerned with relative speed.
  Since both trains are traveling in the same direction their relative speed becomes (50-32)kmph. = 18kmph = 5m/s.
  Now speed * time = length of faster train . So 15s * 5m/s = 75m
• 13 years agoHelpfull: Yes(17) No(0)
• 75m
  because difference in speed of the two trains is 18kmph
  so it is 18*5/18 m/sec
  so 5m/sec
  so distance covered in 15 sec at speed of 5m/sec is 5*15=75m
• 13 years agoHelpfull: Yes(6) No(0)
• 75m
• 13 years agoHelpfull: Yes(3) No(1)
• let the length of faster train is l...
  time taken to cross the person sitting in slower train is 15 sec
  time=faster train length/relative speed
  
  15/(60*60)=l/(50-32)
  on calulating
  length =75 m ANS
• 8 years agoHelpfull: Yes(0) No(0)
• let length of train is x m.
  difference of speed=50-32=18km/h=18*5/18=5m/s
  time=train length/relative speed
  15/60*60=x/5
  x=75
  so length of train is 75 m
  
• 8 years agoHelpfull: Yes(0) No(0)
• speed=50-32=18kmph=18*5/18=5m/s
  speed=length/time
  5=length/15
  length=75m
• 6 years agoHelpfull: Yes(0) No(0)