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Two boxes connected to a string over an ideal pulley?

  • Thread starter algar32
  • Start date
  • #1
89
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Homework Statement


Two blocks are connected by a string that goes over an ideal pulley as shown in the figure and pulls on block A parallel to the surface of the plane. Block A has a mass of 3.00 kg and can slide along a rough plane inclined 30.0° to the horizontal. The coefficient of static friction between block A and the plane is 0.400. What mass should block B have in order to start block A sliding up the plane?


Homework Equations


box A- sum of x & sum of y
box B- sum of y
plug into each other



The Attempt at a Solution


m2=(ms*m1*sin(theta)+m1*cos(theta)
=3.198


Thanks.
 

Answers and Replies

  • #2
157
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First of all. What are all the forces acting upon block A?
 
  • #3
89
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First of all. What are all the forces acting upon block A?
The forces acting on block A are static friction, fnormal, gravity, and ftension.
 
  • #4
157
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Yes. So the friction force and force of gravity are preventing the block from sliding up the ramp. What's next?
 
  • #5
89
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Yes. So the friction force and force of gravity are preventing the block from sliding up the ramp. What's next?
ffriction = -.4*9.81*3
fgrav= -sin30*9.81*3
ftension =m*9.81

ffriction +fgrav = ftension

Not sure which part i messed up
 
Last edited:
  • #6
157
0
ffriction = -.4*9.81*3
Friction force is equal to μF[itex]_{normal}[/itex].
 

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