Dr. Chirdon needs to walk his dog before the surface temperature of the sidewalk reaches 50C. Assume: The sidewalk is very thick and has a temperature of 25C at 6:00AM throughout the slab. The sidewalk has a thermal diffusivity of 7107m2/s and conductivity of 1.3W/mC. The sun heats the sidewalk at a constant rate of 250W/m2 starting at 6:00AM. Neglect any heat loss from radiation or convection. At what time is it too late to walk his dog if the sun rises at 6:00 AM? Dr. Chirdon needs to walk his dog before the surface temperature of the sidewalk reaches 50C. Assume: The sidewalk is very thick and has a temperature of 25C at 6:00AM throughout the slab. The sidewalk has a thermal diffusivity of 7107m2/s and conductivity of 1.3W/mC. The sun heats the sidewalk at a constant rate of 250W/m2 starting at 6:00AM. Neglect any heat loss from radiation or convection. At what time is it too late to walk his dog if the sun rises at 6:00 AM