Problem about finding the work done by friction force

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  • #1
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Homework Statement



A block of mass M=3.4 kg is dragged over a horizontal surface by a force F=20.0 N. The block is displaced a distance d=17.0 m, the friction force Ff is 3.3 N. What is the work done by the friction force?


Homework Equations



Ff=μkFn

The Attempt at a Solution



I solved a problem before this one in finding the applied force but this one is very confusing to me. I have no idea where to even start. Thank you!
 

Answers and Replies

  • #2
Work done by friction is always negative. The work done by a constant force is always the dot product of the force multiplied the displacement whether or not the force is the cause of the displacement. So the work done would be -3.3*17 = -56.1 Joules.
 
  • #3
Why don't we start with recalling how to calculate the work done by any Force?
[itex] \Large W = \int \vec{F} \cdot d\vec{r} [/itex]
We can reduce this to simply:
[itex]
\vec{F}\cdot{\vec{x}}
[/itex]
Now the rest is pretty straightforward in your case.
Hope that takes care of the confusion,
Daniel
 
  • #4
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Thank you so much!!!
 

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