MCAT Work and Friction Problem

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The discussion revolves around a physics problem involving a block sliding to a stop due to friction. The correct answer is identified as D, which states that the work done on the block equals the sum of its changes in kinetic and internal energies. The confusion arises from the interpretation of the work equation, where displacement, not just distance, is crucial. The distinction is made clear through an analogy of rubbing hands together, where work is done despite no displacement. Understanding this concept clarifies why option A is incorrect and highlights the relationship between frictional work and energy changes.
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Homework Statement



A block slides to a stop along a table top. Which of the following statements is true?

A. The work done by friction is equal to the force of friction times the distance that the block slid.
B. The work done on the block is equal to the force of friction times the distance that the block slid.
C. The work done on the table is equal to the force of friction times the distance that the block slid.
D. The work done on the block is equal to the sum of its changes in kinetic and internal energies.

Homework Equations


W = Ffr*d


The Attempt at a Solution


The answer given by the book is D but I do not understand why A is the incorrect answer. I thought if friction is doing work against the direction of motion of the block it would just equal exactly as what is stated - force of friction direction parallel to motion times the distance? As for D, wouldn't it be equivalent to A since whatever changes in potential and kinetic energy would entail and equivalent change in friction?

I'm really new to physics, so I'm missing very key concepts that I am not able to piece together. So thank you for your help and patience.
-Taminem
 
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do you have any image of how the block was sliding ?

work done by friction depend on distance no displacement --- maybe that's why A is wrong coz problem may be referring to displacement
 
Hi cupid.callin,
Thanks for the reply. Turns out there is no image of how the block was sliding. However, your comment made me reread the equation for work and realize why D is the answer and not A. Since, d in the work equation is displacement and not distance, like the phenomenon of rubbing two hands together, no displacement is done since the positions of the hands in the initial state and final state are the same, but work is still done in the form of increasing the internal energy/temperature of the hands at the expense of kinetic mechanical energy. Thus, work done by frictional forces is not just Ffr * d but the change in Eint and mechanical energy.

Thanks for your reply! It was really useful.
 

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