Friction and loss of Potential energy

[Sonyfan08]

BR Physics III # 17: As a mining travel down the rails of a mine, what is true of its relative energies?

Originally, I thought that the PEinitial= PE + KE (at a particular time).. but it turns out that there is friction. Do you always assume that there is friction? Also, it says that "as the cart travels the track, the work down by friction increases." Why does friction increase as you go down the track?

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[kkentm]

W = Fd so im guessing the book is trying to say the work done over time increases due to the increasing displacement of the cart. Also, i believe on the mcat you generally assume frictionless conditions unless explicitly stated.

 

[yankswin2011]

BR Physics III # 17: As a mining travel down the rails of a mine, what is true of its relative energies?

Originally, I thought that the PEinitial= PE + KE (at a particular time).. but it turns out that there is friction. Do you always assume that there is friction? Also, it says that "as the cart travels the track, the work down by friction increases." Why does friction increase as you go down the track?

For some reason, the TBR Physics passages, particularly in the Energy section are poorly worded and missing key information so I would not worry if you got them wrong. The quality of TBR's Chemistry and Orgo are top-notch but for some reason, TBR's Physics passages are filled with typos, errors, and just poorly crafted.