18 CHAP - 18. PROBLEMS ON TRAINS IMPORTANT FACTS AND...

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18. PROBLEMS ON TRAINS IMPORTANT FACTS AND FORMULAE 1. a km/hr= (a* 5/18) m/s. 2. a m / s = (a*18/5) km/hr. 3 Time taken by a train of length 1 metres to pass a pole or a standing man or a signal post is equal to the time taken by the train to cover 1 metres. 4. Time taken by a train of length 1 metres to pass a stationary object of length b metres is the time taken by the train to cover (1 + b) metres. 5. Suppose two trains or two bodies are moving in the same direction at u m / s and v m/s, where u > v, then their relatives speed = (u - v) m / s. 6. Suppose two trains or two bodies are moving in opposite directions at u m / s and v m/s, then their relative speed is = (u + v) m/s. 7. If two trains of length a metres and b metres are moving in opposite directions at u m / s and v m/s, then time taken by the trains to cross each other = (a + b)/(u+v) sec. 8.If two trains of length a metres and b metres are moving in the same direction at u m / s and v m / s, then the time taken by the faster train to cross the slower train = (a+b)/(u-v) sec. 9. If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then (A's speet) : (B’s speed) = (b 1/2 : a 1/2 ).
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SOLVED EXAMPLES Ex.I. A train 100 m long is running at the speed of 30 km / hr. Find the
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18 CHAP - 18. PROBLEMS ON TRAINS IMPORTANT FACTS AND...

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