Two trains A and B are moving with speeds 20 m/s and 30 m/s respectively in
the same direction on the same straight track, with B ahead of A. The engines
are at the front ends. The engine of train A blows a long whistle.
The speed of sound in still air is 340 m/s.
The speed of sound of the whistle is
(A) 340 m/s for passengers in A and 310 m/s for passengers in B
(B) 360 m/s for passengers in A and 310 m/s for passengers in B
(C) 310 m/s for passengers in A and 360 m/s for passengers in B
(D) 340 m/s for passengers in both the trains
11I thought so too...until i saw the answer.....given ans is B
11B)
is the answer
For passenger in Train A
The whistle is blown ahead so the sound has to travel back with 340
While the train is moving with 20m/s in opposite= 360m/s For A
While the passenger in B is ahead of The whistle and the sound travels ahead with 340 while the train is also moving in the same direction therefore 340-30 = 310m/s for B
11isn't it just the concept of relative velocity?? (340-20)ms-1 for A and (340-30)ms-1 for B??
Anonymous No u asshole. Don't teach shit if u don't know shit. U got that?
1if vel. are in same directions they are subtracted and in opp. directions they are added.
11See the sound can travel in all direction.
Now since if you only take the forward direction it will be in correct as according to your method the passenger in A cannot hear it since the sound is moving ahead with velocity faster then itself.
But that is not true .
Therefore you have take the direction in such a way that the sound will be heard by the passenger. Therefore for A the direction will be backward. While for B the direction will be forward
