Question

(i)two trains running in opposite directions at 36 km/hr and 45 km/hr cross each other in 20 s.if one train is 200 m long,the length of another train is
(a) 200 m(b)250 m (c)300 m (d)none
(ii)a train 220 m long is running with a speed of 60 km/hr.in what time will it cross a man who is running at 6 km/hr in direction opposite to that in which the train is going.
(a)12 sec (b)12 min (c)12 hours (d) none
please tell the questions in detail.tell me fast

Answer 1

1)
Relative velocities of the two trains = 36 + 45 = 81 kmph
The time duration for the cross over = 20 sec.
the total distance travelled in 20sec at relative velocity = 81 kmph * 5/18 * 20 sec
       = 450 m

Length of the second train = 450 m - 200 m = 250 meters.
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b)
relative velocity of the train and person = 60 kmph + 6 kmph = 66 kmph
   = 5/18 * 66 = 55/3 m/s
length of distance to cross = length of train = 220 m
time duration to cross = 220 / (55/3) = 12 sec.