Question

Astronauts visiting planet X are trying to measure the gravitational acceleration there. They use a 2.36 m long string of mass 5.3 g,attach it to a support, and stretch it over a pulley L=2.02 m away. A mass M=1.43 kg is tied to the free end. When they excite standing waves on the string, the astronauts find some at 44 Hz and 55 Hz, but not in between. What is the gravitational acceleration on the planet, gx?