Forces on an inclined plane with a pulley

AI Thread Summary
The discussion focuses on calculating the forces acting on a 77.0 kg patient suspended in a hospital bed at an incline, factoring in static and kinetic friction. The initial setup incorrectly equates forces without considering static friction, which is crucial for determining the minimum mass required to keep the patient stationary. Participants suggest incorporating static friction into the equation, emphasizing that the tension in the wire must balance both the gravitational component and the frictional force. The correct approach involves adjusting the equation to include static friction, leading to a more accurate calculation of the necessary mass. Understanding these forces is essential for solving the problem effectively.
kmerr98277
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Homework Statement


A 77.0 kg patient is suspended in a raised hospital bed as shown in the figure. The wire is attached to a brace on the patient's neck and pulls parallel to the bed, and the coefficients of kinetic and static friction between the patient and the bed are 0.500 and 0.800, respectively.
P4-80.jpg

My attempt:
mg sinθ = mg sinθ
(77.0)(9.8)(sin50) = m(9.8)(sin90)
578.057 = m9.8
m = 58.985
I'm not sure if I set that up right. Also, I don't know how to factor in the friction to the equation.
 
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kmerr98277 said:

Homework Statement


A 77.0 kg patient is suspended in a raised hospital bed as shown in the figure. The wire is attached to a brace on the patient's neck and pulls parallel to the bed, and the coefficients of kinetic and static friction between the patient and the bed are 0.500 and 0.800, respectively.
P4-80.jpg

My attempt:
mg sinθ = mg sinθ
(77.0)(9.8)(sin50) = m(9.8)(sin90)
578.057 = m9.8
m = 58.985
I'm not sure if I set that up right. Also, I don't know how to factor in the friction to the equation.
I think what the question wants is the lowest mass that keeps the patient stationary right?
Well you are missing something in your solution.. Static friction.
I think you should add the value of static friction to the right side to the incline
So the equation should be M(Patient) g sin θ = T(which equal to mg) + Us * n (equals mg cosθ)
Imagine that patient is not connected to mass. He would fall right? but what is the counter of the force here static friction... Now try to imagine that you are adding small amount of mass each time to balance out the forces. By the equation you will get the right amount of mass and the lowest

 
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