Astronauts visiting planet X have a cord of length 2.5 m and mass 5.0 g. They attach one end of the rope to a rod of the landing capsule, stretch the rope horizontally over a pulley located 2.0 m away, and hang a mass of 1.0 kg from the free end of the rope. Then they will excite standing waves on the cord. The measurement data shows that standing waves are formed at frequencies of 64 Hz and 80 Hz, but not at intermediate frequencies. What is the value of the gravitational acceleration on planet X? A. 2.0 m/s B. 5.3 m/s C. 8.2 m/s D. 9.4 m/s E. 10.7 m/s F. 12.8 m/s