Sometimes sweat on the firewalker's feet can act as a barrier between the hot coals and his feet. The part of the water droplet that is in contact with the hot surface of the coal absorbs the heat and starts to vaporize. When the water vaporizes, heat energy is transferred from his feet to the atmosphere—thus keeping his feet from burning.

How do you think water (specific heat is 4.18 J/grams • °C) can protect against hot coals (specific heat is 1.70 J/ grams • °C)?

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It takes a lot more energy to change (increase) the temperature of water than it does to change (decrease) the temperature of the hot coals.

You can calculate the amount of energy that is transferred during the man's walk on the hot coals. Complete the calorimetry questions about the firewalker. Let's review the equation for calorimetry.

amount of energy = specific heat  x  mass  x  change in temperature

Dew that is on the grass has gotten on the man's feet as he walked to the hot coals. The water droplets on the man's feet have a temperature of 30.0°C. As the man walks on the coals, the temperature of the water changes to 50.0°C. How much heat was needed to change the temperature of the 7.50 grams of water on the man's feet? (Water has a specific heat of 4.18 J/grams • °C)

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627 J

amount of energy = specific heat  x  mass  x  change in temperature

If you don't have a calculator, you can use the online calculator here.

The hot coals are made from ordinary wood that has a specific heat of 1.700 J/ g • °C. The surface of the coals reaches 600.0°C before the firewalker scurries across them with bare feet. How much energy is required to lower the temperature of a 810.0 gram piece of hot coal from 600.0°C to 599.0°C?

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1,377 J

Amount of Energy = Specific heat  x  mass  x  change in temperature

Earlier in the day, the firewalker went on a strenuous hike in the mountains. His body began to heat up and his temperature rose. His body has a mass of 74.35 kg and his initial body temperature was 98.3°C. If 309.6 J of energy was used to change his body temperature, what was his elevated body temperature to the nearest tenth of a degree? (The specific heat of the human body is 3.470 J/kg • °C.)

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99.5 °C

Amount of Energy = Specific heat  x  mass  x  change in temperature

Once you find the temperature change, you have to add it from the initial temperature to find the final temperature.