A .6 gm peanut is burned beneath 50g of water, which increases the temperature from 22 degrees to 50 degrees centigrade. Assuming 40% efficiency, show that the peanut's food value is 3500 calories.

Answer 1

1 caloris is the amount of energy needed to raise the temp of 1g or water 1 degree.

So if it raises 50g by 28 deg, that's how many calories?

OK, so we know how many calories affected the water, but we are also told that the burning was only 40% efficient, which means that our answer is only 40% of the total energy in the peanut.

Is this enough?

Answer 2

A calorimetric measurement of food value in which the combustion is only 40% efficient does not sound very useful. How can one be sure of the efficiency?

jim has correctly shown you how to do the calculation and get 3500 (gram)-calories. You won't need the peanut's mass since they are not asking for calories per gram. Not that the units are not the Calories usually used for food.

Answer 3

1400