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Advanced: Freefall problems

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A test rocket launches vertically upwards with a constant acceleration of 5 m/s2. After some time t, the rocket's fuel tank goes empty. The rocket still goes 125 m up and only then starts to descend.
How much time did it take for the rocket's tank to go empty?
Note: Take g=10 m/s2.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi