Let the length of the train be 'L' meters and its speed be 'v' meters/sec
Then, L/v = 15
? v = L/15 ....(1)
Now, (L + 100)/25 = L/15
? L = 150 m
Let the speed of the second train be y km/hr
Relative speed of both trains = (50 + y) km/hr
Total distance traveled = 100 + 120 = 220 meters = 0.22 km
Time = 6 sec = 6/( 60 x 60) hr.
Speed = distance/time
? 50 + y = (0.22 x 60 x 60)/ 6
? 50 + y = 132
? y = 82
? Speed of the second train = 82 km/hr
Let the length of the train be L km and its speed by y km/hr
Then , speed of train relative to first man = (y - 2) km/hr
Speed of train relative to second man = (y - 4) km/hr
? L / (y - 2) = 9 /(60 x 60)
and L / (y - 4) = 10/ (60 x 60)
? 9y - 18 = 3600 x L ...(1)
and 10y - 40 = 36000 x L ... (2)
So, 9y - 18 = 10y - 40
? y = 22
? L/ (22 - 2) = 9/ 3600
? L = (20 x 9) / 3600 = 1/20 km = (1/20) x 1000 = 50 m.
Suppose they meet T hrs after 7 a.m
? Distance covered by A in T hrs = (20 x T) km
Distance covered by B in (T - 1) hrs = 25(T - 1) km
? 20T + 25 (T -1) = 110
? 45 x T = 135
? T = 3 hours
So, they meet at 10 a.m.
? Speed of the train = 20 x (5/18) = (50/9) m/sec
? Time taken by the train to pass the man = 75 x (9/50) = 13.5 sec
? Speed = (45 x 5/18) = (25/2) m/sec
Distance = (Time x Speed) = (12 x 25 / 2 ) meters
= 150 meters
? Length of the train = 150 meters
Relative speed of the train = (40 - 22) km/hr = 18 km/hr
Relative speed of the train in m/sec = 18 x (5/18) = 5 m/sec.
Let the length of 2nd train be L meters.
Then, (125 + L) / 5 = 60 sec.
? 125 + L = 300
? L = 175
? Length of second train = 175 meters
Let the speed of the train be v km/hr
Relative speed of the train = (v + 6) km/hr = [(v + 6) x 5/18] m/sec
? 150/6 = (v + 6) x (5/18)
? 5v + 30 = 450
? v = 84 km/hr
? Relative speed of the train = (40 - 25) km/hr = 15 x (5/18) = 25/6 m/sec
? Length of the train = (48 x 25) / 6 = 200 meters .
Relative speed of both trains = (150 + 100)/10 = 25 m/sec = 25 x (18/5) = 90 km/hr
? Speed of second train = (90 - 30) = 60 km/hr .
speed of train = 36 x (5/18) = 10 m/sec.
Let the length of the train be L meters
Then, L/10 = 10
? L = 100 meters.
? Time taken to cross the platform = (100 + 55) / 10 = 151/2 sec.
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