Communication Systems

The critical velocity of satellite of mass $$100 kg$$ moving round a planet is $$20 m/s$$. If another satellite of mass $$200 kg$$ is kept moving in the same orbit then its critical velocity will be:
Explain detection of amplitude modulated wave.
The need for doing modulation is :

What is the name of short duration wave?

Mention the functions of any two of the following used in communication system:
(i) Transducer
(ii) Repeater
(iii) Transmitter
(iv) Bandpass Filter