Navjivan Express fro m Ahmadabad to Chennai leav es Ahmadabad at 06.30 am and
travels at 50 k m/hr towards B aro da situated 100 k m away. At 7 am Howrah to
Ahmadabad express leaves Baroda tow ards Ahmadabad and trav els at 40 km/hr . At
7.30 Mr.John , the t raffic controller at Baro da r ealises that bot h t he trains are r unning
on the s ame t rac k. How much time do es he have to avert a head- o n collision between
the two t rains?
(a) 15 minut es (b) 20 minut es (c) 12 minutes (d) 18 minutes

• distance travel by nav. exp. in 1 hr.= 50*1 = 50 km
  distance travel by hw. ahem. exp. in 1/2 hr = 40*1/2= 20 km
  distance will remain before the collision = 30 km
  relative speeds of trains (50+40)kmph
  so time require before collision= 30/90= 1/3 hr. = 20 min.
  
• 12 years agoHelpfull: Yes(18) No(1)
• we calculate distatnce travelled by both trains till 7-30 am . It comes out to be 50+20=70km. becacuse in half hour second train travels 20 km. so now the distance left between both is 100-70=30... so now time is dist/speed. so time= 30/(50+40)=1/3hour or 1/3*60= 20 min...... ans is 20 min,,,
• 12 years agoHelpfull: Yes(8) No(1)