In physics and chemistry, the law of conservation of energy states that the total energy of an isolated system remains constant; it is said to be conserved over time. This law means that energy can neither be created nor destroyed; rather, it can only be transformed or transferred from one form to another. Ex. Roller coasters and dominos. As a fact, mechanical energy = kinetic energy + ...
The weight on the earth and moon are different. So, the weight obviously will be halved.