Which has more Gravitational Potential Energy: a 7kg lamp on a 6m high shelf or a 4kg book 2 shelves (2m) down?

2 answers

Gravitational Potential Energy = m g h

higher and heavier wins
If we take the Gravitational Potential Energy equation (E=mgh) and apply it to each object, we will see that:

Lamp: E=mgh=(7kg)(9.81m/s^2)(6m)=412.02

Book: E=mgh=(4kg)(9.81m/s^2)(2m)=78.48

So clearly, the lamp has more gravitational potential energy and you didn't even need to do the formula because higher and heavier wins like R_scott said.