Question

speeds of two train ratio 3:4 .they are going in opposition direction along paraell tracks. if each takes 3 sec to cross a telegraph post.find time taken by train to cross each other completely​

Answer 1

Let speed of one train be 3M and other train be 4M.

Speed of one train = 3M

Speed of other train = 4M

Total speed of both the trains = 3M + 4M

=> 7M

Both trains cross the telegraph in 3 sec.

Now,

Length of one train = 3M × 3

=> 9M

Length of other train = 4M × 3

=> 12M

Total length of both the trains while crossing telegraph = 9M + 12M

=> 21M

Now,

Speed = Distance/Time

Time = Distance/Speed

Here.. distance = total length of both the trains

Substitute the known values in above formula

=> Time = 21M/7M

=> Time = 3 sec

∴ Both the trains cross each other in 3 sec.

Answer 2

$\huge\bf{Answer:-}$

3 seconds.

Further Explanation

Accoding to the given question:-

• Let 3 be the speed of one train.

• Let 4 be the speed of other train.

• 3 + 4 => 7 be the speed of both train.

• 3 second is the time of both trains to cross the telegraph.

• Length of one train (3 × 3)=>9

• Length of other train (4 × 3) = 12

• (9 + 12) => 21 is the length of both trains when crossing the telegraph.

Using formula:-

• Speed = Distance/Time

• Time = Distance/Speed

• Let T be the time.

$t = \frac{21}{7}$

Therefore the time taken is 3sec.