576_Physics ProblemsTechnical Physics

576_Physics ProblemsTechnical Physics - 578 Heat and the...

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Unformatted text preview: 578 Heat and the First Law of Thermodynamics Q20.29 The person should add the cream immediately when the coffee is poured. Then the smaller temperature difference between coffee and environment will reduce the rate of energy loss during the several minutes. Q20.30 The cup without the spoon will be warmer. Heat is conducted from the coffee up through the metal. The energy then radiates and convects into the atmosphere. Q20.31 Convection. The bridge deck loses energy rapidly to the air both above it and below it. Q20.32 The marshmallow has very small mass compared to the saliva in the teachers mouth and the surrounding tissues. Mostly air and sugar, the marshmallow also has a low specific heat compared to living matter. Then the marshmallow can zoom up through a large temperature change while causing only a small temperature drop of the teachers mouth. The marshmallow is a foam with closed cells and it carries very little liquid nitrogen into the mouth. The liquid nitrogen still on theclosed cells and it carries very little liquid nitrogen into the mouth....
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