일반물리학 2 — Relativity: Problem 16

16 Stellar system \( Q_1 \) moves away from us at a speed of \( 0.700c \). Stellar system \( Q_2 \), which lies in the same direction in space but is closer to us, moves away from us at speed \( 0.400c \). What multiple of \( c \) gives the speed of \( Q_2 \) as measured by an observer in the reference frame of \( Q_1 \)?