Two events occur 100 m apart with a time interval of 0.60 us between them in frame A. Relative to A, the speed of reference frame B, in which the two events occur at the same
location, is:
a) 0
b) 0.25c
c) 0.56C
d) 1.1c
e) 1.8c

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?