Question about work, friction

[closertofine]

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I keep seeing this type of question on practice tests, and I can never figure out the right answer! How do you find work done by friction? I am using the EK books, but it seems kind of unclear the way they describe it.

 

[Mudd]

It is often easiest to consider the work done by friction equal to the kinetic energy lost by the system over whatever distance the friction is applied.

 

[GATORade]

From what I remember, W=F*D. Therefore, I would imagine the easiest way to calculate the work done by friction would be to multiply the force of friction (coefficient of kinetic friction * normal force) by the distance in which the object travels. Also, if you are given the work done on an object, the distance traveled and the force applied, use the above equation to see if the amount of work given matches the amount of work calculated. If not, the difference between the calculated work and work given is the work lost, or done by friction.

I hope my choppy explanation didn?t confuse you even more.

Good luck.