The energy content of food is usually given in Calories. One Calorie is equal to 4186 J. Suppose a person uses 2000 Calories in a day to keep his vital organs functioning.

2000 Calories = 837,200 J

To find out how much energy in joules is used, we need to convert the 2000 Calories into joules. We know that one Calorie is equal to 4186 J.

So, we can calculate the energy used in joules as follows:

Energy (joules) = 2000 Calories * 4186 J/Calorie

Let's calculate it:

Energy (joules) = 2000 * 4186 = 8,372,000 joules

Therefore, the energy used by a person in joules to keep his vital organs functioning is 8,372,000 joules.

To find out how much energy is used in joules, we need to convert the energy from Calories to joules.

Given:
1 Calorie = 4186 J

We are told that the person uses 2000 Calories in a day. Therefore, we can calculate the energy used in joules by multiplying the number of Calories by the conversion factor:

Energy used (in joules) = 2000 Calories × 4186 J/Calorie

Now, let's calculate the result:

Energy used (in joules) = 836,000 J

Therefore, a person who uses 2000 Calories in a day to keep his vital organs functioning uses approximately 836,000 joules of energy.