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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)/(uv) 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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View Full DocumentSOLVED EXAMPLES
Ex.I. A train 100 m long is running at the speed of 30 km / hr. Find the
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 Spring '11
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