[单选题]
A spear is thrown by you at a very high speed. As it passes, you vw-+qu k ,wi ttdo0d17mea fod05i/p md8ahbu5 8gsure its length at one-half its normal length. From this measurement, you conclude that the moving sbhd/0g u85 8mpa dof5ipear's mass must be
A. one-half its rest mass.
B. twice its rest mass.
C. four times its rest mass.
D. none of the given answers
Post time 2024-1-14 16:03:04