A 600,000 kg subway train is brought to a stop from a speed of 0.5 m/s by a large spring bumper at the end of
its track which compresses 0.4 m. This transfer of
energy has been loaded onto the spring. What is the
spring constant of the bumper?

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The “death throes” of stars are amongst the most complex phenomena in all of astronomy, and the “corpses” of stars amongst the most energetic and exotic objects in existence. beginning at the end of the core helium fusion stage in a star’s life, describe in detail the post-main sequence development of both (a) a 1.0 solar mass star, and (b) a 25.0 solar mass star. in what significant ways do they differ? what role does each of these types of stars play in the "star-gas-star" cycle and the evolution of chemical elements in our galaxy?

According to social exchange theory, altruistic behaviors benefit the individual who performs them. t/f

Which is the correct symbol for an isotope of iodine with 53 protons and 78 neutrons?