Friction - static question

  • Thread starter jjesiee
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  • #1
jjesiee
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Homework Statement




A 4.0 kg block of wood sits on a table. A string is tied to the wood,
running over a pulley and down to a hanging object. The greatest mass that can be
hung from the string without moving the block of wood is 1.8 kg. Calculate the coefficient
of static friction between the block of wood and the table.

4.0 kg and 1.8 kg- mass

Homework Equations



Fs=μFn

The Attempt at a Solution



so i assume the block isnt moving so fnet would be 0, fn=fg so 4.0(9.8) ---> 39.2

i dont have fs and mew so how am i supposed to solve this?
 

Answers and Replies

  • #2
PhanthomJay
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There are 2 forces acting horizontally on the block on the table. One is the tension force that can be calculated by looking at the forces on the hanging mass.
 
  • #3
vishavs
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It is always best to create a diagram and Net force equations for each individual object. You are right in that F=0 but this also tells you that whatever force is pulling at the block of wood, there is an equal and opposite force that stops it from moving. This is crucial piece of information for your problem.
 
  • #4
jjesiee
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so if i calculate fg=mg on the hanging mass, would the force of tension be the same as fg?
 
  • #5
PhanthomJay
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so if i calculate fg=mg on the hanging mass, would the force of tension be the same as fg?
Sure!
 

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