# Relativity space travel and relativistic momentum

1. A ball (B) of mass m moves with velocity v relative to an observer (O). The momentum of B relative to O is p=mv according to Newtonian mechanics and p=gamma x mv according to Special Relativity. What do the above two theories predict for B's momentum if its speed equals c, the speed of light?

2. Alice travels from Earth to a distant star that is 25 light years away. One light year is the distance that light propagates in one year. Bob stays at home on Earth. Alice moves at v=0.9998c relative to Bob. The gamma factor is 50. How far has Alice traveled according to (i) her measurements and (ii) those of Bob?

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I have solved two relativity problems which deal with the distance traveled by a space traveler with a velocity closed to the speed of light and the relativistic momentum.