Question

A train cross B train within 50sec and they cross each other within 20sec thier length 160m and 240m respectively. how many time takes by both trains to cross a bridge 420m

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Answer 1

When train A cross train B

Total distance(d) = 160+240 = 400m

Time(t) = 50 sec

Speed (s) of train A= d÷t = 400 ÷50 = 8 m/sec (

When train A and B cross each other

Distance (d)= 160+240 = 400m

Time(t) = 20

Speed of train A = 8 m/sec ( from above)

Let Speed of train B = x m/sec

Speed (relative speed ) = speed of train A + speed of train B = (8+x)m/s

So, (400÷20)=(8+x) =》20 =8+x =》20-8=x =》 12 =x

When train A crosses tunnel

Distance = 240 + 160 = 400m

speed = 8m/sec

Time = 400÷8 = 50 sec

When train B crosses tunnel

Distance = 240+240 =480 m

Speed = 12 m/sec

Time = 480÷12 = 40 sec