The Quantity Which Does Not Change in Magnitude from That $\overrightarrow { \mathbf { a } }$

Multiple Choice

The quantity which does not change in magnitude from that observed in system S when observed in system S' moving away from system S at speed v is

A) m $\overrightarrow { \mathbf { a } }$ .
B) m $\overrightarrow { \mathbf { v } }$ .
C) ( $\gamma$ - 1) mc².
D) E² -p²c².
E) x² + y² + z².