A hot concrete slab comes from a furnace at an inatial temperature of 85 C. To cool down the slab, its surface is suddenly exposed to a cold liquid at 5°C. Find the time required for the concrete to cool down to 45 °C at a depth of 5 cm from the surface? Consider thermal diffusivity of concrete 6.5 x 10-7 m/s.

A hot concrete slab comes from a furnace at an inatial temperature of 85 C. To cool down the slab, its surface is suddenly exposed to a cold liquid at 5°C. Find the time required for the concrete to cool down to 45 °C at a depth of 5 cm from the surface? Consider thermal diffusivity of concrete 6.5 x 10-7 m/s.