A scientist sets up a miniature laboratory on the surface of the Moon. She has carried with her a beam balance and a spring balance, along with a sealed box whose true mass on Earth is exactly 2kg.
(i) Which of the two instruments should she select to measure the mass of the box as accurately as possible on the Moon?
(ii) Explain clearly why this instrument will give the correct mass even though the value of acceleration due to gravity on the Moon is different from that on Earth.
(iii) What qualitative change (increase, decrease or no change) would be observed in the reading of the other instrument? Give a reason for your answer referring to the principle of its working.