For a safe re-entry into the Earth's atmosphere, the pilots of a space capsule must reduce their speed from 2.6 x 10^4 m/s to 1.1 x 10^4 m/s. The rocket engine produces a backward force on the capsule of 1.8 x 10^5 N. The mass of the capsule is 3800 kg. For how long must they fire their engine? [Hint: Ignore the change in mass of the capsule due to the expulsion of exhaust gases.] The answer to this problem is 320 seconds, but I have no idea how to get to that answer. I just want to know the formula or theorem that I can use to solve this specific problem. Your help would be highly appreciate. PS. sorry for my English, I'm not a native speaker.