i) For a body executing free vibrations, the graph between displacement and the time is as shown below:

ii) The oscillations of  a body, when set into vibrations by any external force, and then left to itself, executes free vibrations.
For example, a tuning fork when stuck with a hammer starts vibrating and it continues to vibrate for a while.  

i) The sound level 30 dB to 10 dB has the soothing sensation.

ii) Quality (or timbre)                                                                            

i) Total distance travelled by the sound in going and coming back = 2 x 480 m.
Speed of sound =
Time taken to reach second echo = 3+ 2 = 5 sec
Therefore, v =  
 
ii) Distance of other cliff from the person = 

i) B and D would be in a state of forced vibration.

ii) Since the length of the pendulum, C is same as that of A, therefore, it is in the state of resonance.

iii) The pendulum C has its length same as that of A, therefore, its natural time period is also same that of a and both remain in the same phase so resonance takes place. But, B’s length is lesser than the length of A, hence B would vibrate with smaller amplitude.