A tourist carries a spring balance, calibrated in kilograms at the Earth’s surface, to the surface of the Moon where the acceleration due to gravity is 1.63m s−2. He suspends a rock specimen, and the balance pointer comes to rest at the 9\,kg mark.
(a) What is the true weight of the rock on the Moon in newtons?
(b) What is the actual mass of the rock?
(c) If the balance spring has a stiffness constant of 800N m−1, calculate the extension of the spring produced by the rock on the Moon.