A student eats 2000 kcal per day. (a) Assuming that all of the food energy is released as heat, what is the rate of heat released (in watts)? (b) What is the rate of change of entropy of the surroundings if all of the heat is released into air at room temperature \(\left(20^{\circ} \mathrm{C}\right) ?\)

Short Answer

Expert verified
Question: Calculate (a) the rate of heat released in watts and (b) the rate of change of entropy of the surroundings when a student consumes 2000 kcal per day and the heat is released into the air at room temperature (20°C). Answer: (a) The rate of heat released is approximately 96.85 W. (b) The rate of change of entropy of the surroundings is approximately 0.3306 W/K.

Step by step solution

01

Convert Calories to Joules

First, we need to convert the 2000 kcal into joules. Recall that 1 kcal = 4184 J. So we have: 2000 kcal/day × (4184 J/kcal) = 8,368,000 J/day
02

Convert the Energy to Power

To find the rate of heat released in watts, we need to convert joules to watts. Recall that power (W) is energy per unit time (J/s), and we are given energy per day. Since 1 day = 86400 seconds, we can use the following conversion: 8,368,000 J/day × (1 day/86400 s) = 96.85185 W
03

Calculate the Rate of Change of Entropy

We are given the room temperature as 20°C, which we need to convert to Kelvin. The Kelvin temperature can be found by adding 273.15 to the Celsius temperature: \(T = 20 + 273.15 = 293.15 K\) Now, we can use the following formula to find the rate of change of entropy: \(\frac{dS}{dt} = \frac{P}{T}\) where \(\frac{dS}{dt}\) is the rate of change of entropy, \(P\) is the power in watts, and \(T\) is the temperature in Kelvin. Substitute our calculated values into the formula: \(\frac{dS}{dt} = \frac{96.85185 W}{293.15 K} = 0.3306 \frac{W}{K}\) #Conclusion# The rate of heat released as the student consumes 2000 kcal per day is approximately 96.85 W, and the rate of change of entropy of the surroundings is approximately 0.3306 W/K.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

An ideal gas is heated at a constant pressure of $2.0 \times 10^{5} \mathrm{Pa}\( from a temperature of \)-73^{\circ} \mathrm{C}$ to a temperature of \(+27^{\circ} \mathrm{C}\). The initial volume of the gas is $0.10 \mathrm{m}^{3} .\( The heat energy supplied to the gas in this process is \)25 \mathrm{kJ} .$ What is the increase in internal energy of the gas?
Calculate the maximum possible efficiency of a heat engine that uses surface lake water at \(18.0^{\circ} \mathrm{C}\) as a source of heat and rejects waste heat to the water \(0.100 \mathrm{km}\) below the surface where the temperature is \(4.0^{\circ} \mathrm{C}\).
A coal-fired electrical generating station can use a higher \(T_{\mathrm{H}}\) than a nuclear plant; for safety reasons the core of a nuclear reactor is not allowed to get as hot as coal. Suppose that $T_{\mathrm{H}}=727^{\circ} \mathrm{C}\( for a coal station but \)T_{\mathrm{H}}=527^{\circ} \mathrm{C}$ for a nuclear station. Both power plants exhaust waste heat into a lake at \(T_{\mathrm{C}}=27^{\circ} \mathrm{C} .\) How much waste heat does each plant exhaust into the lake to produce \(1.00 \mathrm{MJ}\) of electricity? Assume both operate as reversible engines.
An engine operates between temperatures of \(650 \mathrm{K}\) and $350 \mathrm{K}\( at \)65.0 \%$ of its maximum possible efficiency. (a) What is the efficiency of this engine? (b) If $6.3 \times 10^{3} \mathrm{J}$ is exhausted to the low temperature reservoir, how much work does the engine do?
Show that in a reversible engine the amount of heat \(Q_{C}\) exhausted to the cold reservoir is related to the net work done \(W_{\text {net }}\) by $$ Q_{\mathrm{C}}=\frac{T_{\mathrm{C}}}{T_{\mathrm{H}}-T_{\mathrm{C}}} W_{\mathrm{net}} $$
See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free