This is the major topic in any competitive examinations. So, I am now
explaining the shortcut and the fastest method for solving these problems.
There are four different types of problems in this topic.
They are: 1. Problems on Time taken by train
They are: 1. Problems on Time taken by train
2. Problems on Distance
covered by train
3. Problems on speed of train
4. Problems on 2 trains in
same direction
5. Problems on 2 trains in
opposite direction
6. Problems on finding Length
of train or platform
7. Problems on platform crossing
time
8. Average speeds
You all know this basic Triangle.
/\
/ D \
/ T
| S \
D – Distance , T – Time, S – Speed , L – length of train, Lp –
Platform length
Where d=t *s
T=
d/s
S=
d/t
Time calculated when distance and speed
is given : t=d/s
When
length (l) and speed is given : t= l/s (pole/man crossing time)
Time taken to cross platform : (L+Lp)/s
Relative speeds : Same direction =
(S1 – S2) ; (where s1 >s2)
:
Opposite direction = (S1+S2)
Time taken by trains cross in same
direction is (sum of lengths of trains / diff in speeds)
Time at which 2 trains pass by is (Sum
of lengths / sum of speeds)
Important NOTE:
Conversions: 18 kmph = 5mps
10
mts --->1kmph ---> 36 sec
20
mts ---> 2kmph ---> 36 sec
30
mts ---> 3kmph ---> 36 sec and so on..
Ie, a vehicle travels 10 meters
distance with 1kmph speed in 36 seconds
Vehicle travels 20 meters distance
with 2kmph speed in 36 seconds
Vehicle travels 30 meters distance
with 3kmph speed in 36 seconds
Vehicle travels 40 meters distance
with 4kmph speed in 36 seconds and so on..
Now, we will see how to use the
above shortcut.
A car travels with a speed of 108kmph.
What distance will be covered in 15 sec?
Ans : 450mts
Solution: Write the given parameters
in above format
1080mts --> 108 kmph ---> 36sec
Now we know distance travelled in 36
sec. Find 15sec distance using this.
Ie by Ratio method as i
already mentioned in my previous posts Ratio and Proportion
36 --> 1080
15 --> ?? (450)
Average speeds:
When distance is constant ie speeds
are given : 2ab/ (a+b)
When distances and times are given : Total distance/ Total time
Try some problems and Answer them:
1.90kmph in m/s
2.52m/s in kmph
3.A vehicle covers a distance
of 600mts in 2 mins. What is Speed in kmph
4.A car runs at 78kmph. What is
the distance covered in 1min 12 sec?
5.At what time car travels over
a distance of 420mts, if it runs at 90kmph?
6.The ratio between two trains’
speeds is 7:8. If second train runs 400kmph in 5hrs, the speed of first train
is?
7.Speeds of A and B are in
ration 3:4. A takes 20 mins more than B to reach the destination. Then What is
time taken by A and B to reach the destination?
Back to you soon...
