How does the calorie compare to the metric unit the joule? how do you calculate a calorie? is it the same for all types of food?

One calorie is an energy unit of measure equal to about 4.184 joules. As such calorie is a fixed amout of energy and is the same for all types of food.

Explanation:

A calorie is defined as the amount of heat that must supplied to 1 gram of liquid water to increase its temperature 1°C.

The unit calore was established for the metric system, but the current standard SI system of measures use the joule as the the unit for energy.

As said the equivalence between calories and joules is 1 cal = 4.184 joules.

The energy content of the food is usually referred as calories, although it is really kilo calories. For instance, when you say that a snack contains 250 calories, it actually has 250 kilocalories (250,000 calories).

Food calories (the energy content of food) may be measured with a calorimeter, which is the original method. A calorimeter is a device  utilised to burn a sample of food and measure the temperature change in the surrounding water. Although you can use that method in a laboratory, nowadays the energy content is measured indirectly by adding up the energy provided by the energy-containing nutrients (protein, carbohydrates and fats).

no, the red giant is the hottest with 2.00.000.000 degrees celsius. while the white dwarf only 25,000 degrees celsius.

a corroding iron, if that's one of your choices