Problem 13

Why does tile feel so much colder to your feet after a bath than a bath rug? Why is this effect more striking when your feet are cold?

Problem 14

Can you think of a way to make a blackbody, a material that absorbs essentially all of the radiant energy falling in it, if you only have a material that reflects half the radiant energy that falls on it?

Problem 17

Why is a dry, fluffy coat a better insulator than the same coat when it is wet?

Problem 18

It has been proposed that global warming could be offset by dispersing large quantities of dust in the upper atmosphere. Why would this work, and how?

Problem 19

A thermos bottle fitted with a piston is filled with a gas. Since the thermos bottle is well insulated, no heat can enter or leave it. The piston is pushed in, compressing the gas. a) What happens to the pressure of the gas? Does it increase, decrease, or stay the same? b) What happens to the temperature of the gas? Does it increase, decrease, or stay the same? c) Do any other properties of the gas change?

Problem 20

How would the rate of heat transfer between a thermal reservoir at a higher temperature and one at a lower temperature differ if the reservoirs were in contact with a 10 -cm-long glass rod instead of a 10 -m-long aluminum rod having an identical cross-sectional area?

Problem 21

Why might a hiker prefer a plastic bottle to an old-fashioned aluminum canteen for carrying his drinking water?

Problem 23

You are going to lift an elephant (mass \(\left.=5.0 \cdot 10^{3} \mathrm{~kg}\right)\) over your head \((2.0 \mathrm{~m}\) vertical displacement). a) Calculate the work required to do this. You will lift the elephant slowly (no tossing of the elephant allowed!). If you want, you can use a pulley system. (As you saw in Chapter \(5,\) this does not change the energy required to lift the elephant, but it definitely reduces the force required to do so.) b) How many doughnuts ( 250 food calories each) must you metabolize to supply the energy for this feat?

Problem 24

A gas has an initial volume of \(2.00 \mathrm{~m}^{3}\). It is expanded to three times its original volume through a process for which \(P=\alpha V^{3},\) with \(\alpha=4.00 \mathrm{~N} / \mathrm{m}^{11} .\) How much work is done by the expanding gas?

Problem 26

The internal energy of a gas is \(500 .\) J. The gas is compressed adiabatically, and its volume decreases by \(100 . \mathrm{cm}^{3} .\) If the pressure applied on the gas during compression is \(3.00 \mathrm{~atm},\) what is the internal energy of the gas after the adiabatic compression?

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