Fire walking. A man strides across a bed of glowing embers as seen in Figure P14.71, and...

Fire walking. A man strides across a bed of glowing embers as seen in Figure P14.71, and due to some very specific physical circumstances, he emerges with no physical harm. Assume the glowing charcoal is covered with a thin layer of ash 0.50 mm thick and is at a temperature of 650°C. The thermal conductivity of ash and charcoal is approximately 1.5 W/(m · K). (a) Estimate the heat transferred to the feet of the firewalker as he traverses the bed of embers in six quick steps. Assume the area of the bottom of each foot comes into only 50% contact with the embers (a rough surface) and the contact lasts 0.10 s for each step. Is the quantity of heat transferred great or small? (b) Assume he steps onto the fi re from slightly wet grass. If his feet are protected by the conversion of water from a liquid to a gas, how much water is needed to carry away the heat from part (a)? (c) How thick would this layer of water on the sole of each foot need to be? (d) Describe what would happen if instead he were to take the same six quick steps across a slab of iron at the same temperature.