M4maths Previous Puzzles

04 Jan 2010 train speed?

Two trains A and B are moving in opposite direction in different tracks. The length of these trains are 100 m.
and 110 m. respectively. If speeds of A and B are in the ratio 4:5 and these two trains cross each other in 10 sec.
Then speed of train B is

OPtion

1) 70/3 m/s
2) 5/3 m/s
3) 50/9 m/s
4) 55/3 m/s
5) 35/3 m/s
6) 28/3 m/s
7) 4/3 m/s
8) 40/9 m/s
9) 84 m/s
10) 105 m/s

Solution

Let the speeds of the trains are 4v and 5v. Since the trains are moving in opposite direction,
relative speed of the train is 4v + 5v = 9v
According to the formula
speed = distance / time
9v = 210/10 = 21
or v = 7/3 hence speed of B is 5v = 5*7/3 = 35/3 m/s

Correct Option: 5 Best Solution (4)

Dr.Dipin Singh   15 years AGO

The trains will cross each other with relative speed equal to sum of speed of two trains.

Relative speed = sum of length of trains/ time taken to cross each other = 210/10 = 21 m/sec

so sum of speeds = 21 m/sec
rato of speeds = 4:5

speed of train B= 21x5/9 = 35/3 m/sec..


option 5

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rajendra   15 years AGO

total length to be covered =210
time taken=10sec
so length in 1 sec=21meter covered
total speed=21/9*5=35/3m/s is the speed of train b

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Dimple   15 years AGO

Time taken to cross each other or to travel distance of 210 M = 10secs

Sum of their speeds = 210/10=21 m/sec
speed of train B = 21*5/9= 35/3 m/sec ....option 5

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Dr. Divya   15 years AGO

Relative speed of trains = sum of speed of trains = 210/10=21 m/sec
As speed are in ratio of 4:5,

speed of train B= 21*5/9 = 35/3 m/sec

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