[填空题]
Suppose a spacecraft of mass 27,000 kg is accelerateoc7yel l- b4vk:o0f9ds/dx2tpr-si ; d nwt-, lan:d84vb7aa h )2omlqto 0.21c.
(a) How much kinetic energy would it have? KE = $ \times 10^{19} \, \text{J}$
(b) If you used the classical formula for kinetic energy, by what percentage would you be in error? %
