Physics  heat
posted by Mary on .
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.

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? 
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. 
1400