Force problem with three masses and two pulleys

  • #1

Homework Statement


For the apparatus in the figure, what is the minimum value of the coefficient of static friction between the block (m3) and the table that would keep the system at rest if m1 = 0.10 kg, m2 = 0.20 kg, and m3 = 0.30 kg? (Assume ideal conditions for the string and pulleys.)

Homework Equations


F=ma
a= Fnet/mtotal

The Attempt at a Solution


This assignment is extra credit since we havent been taught how to solve these problems yet. I watched multiple three mass, two pulley videos.They are all solving for acceleration with the mu value. I tried using what I saw to adjust to my situation.

I attempted using the formula a=Fnet/Mtotal
a=((4kg)(9.8m/s^2)-(1kg)(9.8m/s^2)(mu)-(2kg)(9.8m/s^2))/7kg

I plugged in my known values
a=(39.2−(9.8)(μ)−19.6)/7

I then moved my 7 over to the a
7a=39.2−(9.8)(μ)−19.6

I am assuming that I should be able calculate acceleration with my known values since I'm solving for mu but haven't figured out the steps to do so
 

Answers and Replies

  • #2
kuruman
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Hi Dayanara Avilez and welcome to PF.

Can you please post the figure? Without it it's hard to check your work.
 
  • #3
phinds
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Probably be easier to help you if you actually posted the figure you are referencing
 
  • #5
haruspex
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a=((4kg)(9.8m/s^2)-(1kg)(9.8m/s^2)(mu)-(2kg)(9.8m/s^2))/7kg
These masses do not match your problem statement.
Also, you seem to be calculating the acceleration that would occur without friction. In this question, there is just enough friction to prevent acceleration. So how strong is the frictional force?
 

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