In exercising, a weight lifter loses 0.236 kg of water through evaporation, the heat required to evaporate the water coming from the weight lifter's body. The work done in lifting weights is 1.41 x 105 J. (a) Assuming that the latent heat of vaporization of perspiration is 2.42 x 106 J/kg, find the change in the internal energy of the weight lifter. (b) Determine the minimum number of nutritional Calories of food that must be consumed to replace the loss of internal energy. (1 nutritional Calorie = 4186 J).
I got (a) right with the answer of -712120 J. But I'm stuck on part b)
I just divide Q = (0.236)*(2.42x10^6) = 571,120 by 4186 and i get = 571120/4186 = 136.44, but this answer is wrong. Any ideas please ?
To determine the minimum number of nutritional calories of food that must be consumed to replace the loss of internal energy, we need to convert the change in internal energy from joules to calories.
In part (a), we found that the change in internal energy of the weight lifter is -712120 J.
To convert this value to calories, we use the conversion factor that 1 nutritional calorie is equal to 4186 J.
So the change in internal energy in calories is given by:
-712120 J / 4186 J/cal = -170.21 cal
However, the negative sign indicates that energy has been lost. We need to consider the absolute value. Therefore, the change in internal energy in calories is 170.21 cal.
This means that the weight lifter needs to consume at least 170.21 nutritional calories of food to replace the loss of internal energy.