The fundamental frequency of a closed organ pipe is equal to the first overtone frequency of an open organ pipe. If length of the open pipe is $$60 \mathrm{~cm}$$, the length of the closed pipe will be:

A car P travelling at $$20 \mathrm{~ms}^{-1}$$ sounds its horn at a frequency of $$400 \mathrm{~Hz}$$. Another car $$\mathrm{Q}$$ is travelling behind the first car in the same direction with a velocity $$40 \mathrm{~ms}^{-1}$$. The frequency heard by the passenger of the car $$\mathrm{Q}$$ is approximately [Take, velocity of sound $$=360 \mathrm{~ms}^{-1}$$ ]

For a periodic motion represented by the equation

$$y=\sin \omega \mathrm{t}+\cos \omega \mathrm{t}$$

the amplitude of the motion is

The engine of a train moving with speed $$10 \mathrm{~ms}^{-1}$$ towards a platform sounds a whistle at frequency $$400 \mathrm{~Hz}$$. The frequency heard by a passenger inside the train is: (neglect air speed. Speed of sound in air $$=330 \mathrm{~ms}^{-1}$$ )