A uniform solid block has weight 500 N, width 0.4 m and height 0.6 m. The block rests on the edge of a step of depth 0.8 m, as shown. [Figure showing a block resting on a step. Part of the block is on the step, part overhangs. Dimensions: block width 0.4m, height 0.6m. Step depth 0.8m. Overhanging part implies the block is initially horizontal with 0.4m width on the step.] The block is knocked over the edge of the step and rotates through 90° before coming to rest with the 0.6 m edge horizontal. What is the change in gravitational potential energy of the block?