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Perhaps, it would be good to update the inset box about impacts using momentum instead of energy equations, especially the part about hitting a snowflake at high velocity. As a mechanical engineer, in dynamics courses, we use impulse momentum to analyze collisions rather than energy equations. Energy is certainly the right analysis for interstellar travel, but the bit about collisions should be done using m1v1 + fdt = m2v2. To accelerate a 0.1 mg snow flake up to 0.1*c in (generously) 1 ms, from rest would require a force of f = 3 x 107 N which would convert to the weight of about 300 elephants to give it meaning to non-technical folks.
Thank you for your comments. I am not sure how to relate momentum to nuclear explosions though. Also, momentum is useful for determining how the velocities are changed by the impact, but in this case, energy is most useful because it kinetic energy must be converted to something else upon impact.