Describe an experiment to prove the law of reflection of sound.

The given graph shows the displacement versus time relation for a disturbance travelling with a velocity of $1500 {\mathrm{ms}}^{-1}$. Calculate the wavelength of the disturbance.

Which of the two graphs (i) and (ii) representing the human voice is likely to be the male voice? Give reason for your answer.    

A girl is sitting in the middle of a park of dimension $12 \mathrm{m}\times 12 \mathrm{m}$. On the left side of it, there is a building adjoining the park and on the right side of the park, there is a road adjoining the park. A sound is produced on the road by a cracker. Is it possible for the girl to hear the echo of this sound? Explain your answer.