Two trains,each 100 m long, moving in opposite directions, cross each other in 8 seconds. If one is moving twice as fast the other, then the speed of the faster train is : A. 30 km /hr B. 45 km / hr C. 60 km / hr D. 75 km / hr
Let speed of faster train be 'x' m/s .
Speed of other train 'y' .
x = 2y .
Relative Dist = 100+100 = 200 m.
Relative speed = x + y = 2y + y = 3y .
Time taken = 8 sec .
Dist / speed = time
200 / 3y = 8 .
y = 200/24 = 25/3 .
.'. x = 2y = 2*25/3 = 50/3 .
.'. Speed of faster train in km/hr = 50/3 * ( 18/5)
= 60 km/hr.