Giancoli's Physics: Principles with Applications, 7th Edition
6
Work and Energy
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6-1: Work, Constant Force
6-2: Work, Varying Force
6-3: Kinetic Energy; Work-Energy Principle
6-4 and 6-5: Potential Energy
6-6 and 6-7: Conservation of Mechanical Energy
6-8 and 6-9: Law of Conservation of Energy
6-10: Power

Question by Giancoli, Douglas C., Physics: Principles with Applications, 7th Ed., ©2014, Reprinted by permission of Pearson Education Inc., New York.
Problem 46
Q

# Two railroad cars, each of mass 66,000 kg, are traveling 85 km/h toward each other. They collide head-on and come to rest. How much thermal energy is produced in this collision?

A
$3.7\times10^7\textrm{ J}$

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VIDEO TRANSCRIPT

This is Giancoli Answers with Mr. Dychko. All of the kinetic energy that the two trains have is going to get converted into thermal energy because they come to a stop and none of that kinetic energy has turned into potential energy, we assume, and so it all becomes thermal. So we take the kinetic energy of one of the trains and since there are two of them, we multiply by 2. So we have one-half times the mass of a single train times its velocity squared times for two trains and that gives us m v squared is our formula for thermal energy. The 66,000 kilograms times 85 kilometers per hour converted into meters per second by dividing by 3.6 and we square that speed and that gets 3.7 times 10 to the 7 joules of thermal energy after the crash.

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