Your uncle works at the railroad freight yard, and he has asked you to watch the
ID: 2077134 • Letter: Y
Question
Your uncle works at the railroad freight yard, and he has asked you to watch the yard hands couple 25,000- kg boxcars together. As he leaves to get a sandwich, he tells you, "Whatever you do, don't let those cars bang together too hard. The coupling between the cars will take only 7,000 J on a hit before it shatters." You ask how hard is too hard, but your uncle has already ducked out. Part A How fast can one moving car bump into a stationary car without the coupling shattering? Express your answer to two significant digits and include the appropriate units.
Explanation / Answer
The energy released = change in kinetic energy of the system
=> 7,000 = (1/2)m[v2 - u2]
assume u = 0 m/s
=> 7000 = (1/2)(7000)v2
=> v = 0.7483 m/s = 0.75 m/s [upto 2 significant figures].
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