(a) Define the “proper time” and “proper length”. (b) Twofighter jets (A and B) are approaching each other. (i) If the speedof each relative to Earth is 0.9 c, (c=speed of light) what is therelative velocity of “A” to that of the “B” and vice versa? (ii) Onthe other hand, if their speeds relative to Earth are 30,000km/h(almost 30 times the speed of the sound) what will be their speedsrelative to each other? (C) The relativistic momentum in each frameis expressed as p=γmu Under what conditions the classical formulafor momentum is recovered?