Two solid sandcastle blocks are to be placed on damp beach sand.
(a) Block X has a mass of 20 kg and a rectangular base of 25 cm × 20 cm. Block Y has a mass of 15 kg with a square base of side 15 cm. The sand begins to sink if the pressure exceeds 6 kPa.
(i) For each block, calculate the pressure it would exert on the sand.
(b) (ii) Identify which block, if any, will sink into the sand and justify your answer with calculations.
(c) (iii) For the block that sinks, determine the minimum area of a thin wooden board that must be placed under it so that the pressure on the sand does not exceed 6 kPa.
(d) (iv) Suggest one practical modification (other than adding a board) that could be made to the sinking block to reduce the pressure it exerts, and explain qualitatively how your suggestion achieves the desired effect.