Cable car with 2 cable arrangement

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SUMMARY

The discussion centers on the mechanics of a two-cable arrangement used in the century-old ascensores of Valparaiso, Chile. The cars, each with a mass of 1600 kg, utilize one cable for connection and another for motorized movement to counteract friction, which has a coefficient of 0.03. The key equations involve Newton's second law, where the net force is zero due to constant speed. Participants explore the tension in both the connecting cable and the motor cable, emphasizing the need to analyze the forces acting on each car separately to resolve confusion regarding their interactions.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Familiarity with free body diagrams (FBDs)
  • Knowledge of friction coefficients and their effects on motion
  • Basic principles of mechanical systems involving pulleys
NEXT STEPS
  • Calculate the tension in the connecting cable using the formula T = 0.03 * cos(35°) * m * g + sin(35°) * m * g
  • Analyze the forces acting on each cable car separately using free body diagrams
  • Research the effects of friction in mechanical systems and how it influences tension
  • Explore the principles of pulley systems and their applications in engineering
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as engineers and designers working with cable systems and pulley arrangements.

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Homework Statement


The century-old ascensores in Valparaiso, Chile, are small cable cars that go up and down the steep hillsides. As the figure(Figure 1) shows, one car ascends as the other descends. The cars use a two-cable arrangement to compensate for friction; one cable passing around a large pulley connects the cars, the second is pulled by a small motor. Suppose the mass of both cars (with passengers) is 1600 kg , the coefficient of rolling friction is 3.0×10−2, and the cars move at constant speed.

What is the tension in the connecting cable?
What is the tension in the cable to the motor?
https://session.masteringphysics.com/problemAsset/1383182/3/07.P43.jpg

Homework Equations


F=ma,since a=0, Fnet=0

The Attempt at a Solution


I drew a free body diagram on both of the cable cars, since F net=0, I was assuming that the x component of all the forces are 0, which are the rolling friction and the x component of the gravitational force. I also assumed that since both cars are 1600kg one's mass would be 800kg? with the rolling friction provided I thought the answer would be 0.03 cos 35 degree*m*g+sin 35 degree*m*g=T, but it seems to be incorrect.
Also I was just completely confused on the effect of the cable between the motor and one of the car. Does it pull the car up? although it appears on the picture that gravity from one car was pulling the other on up?
Thank you.
 
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Look at it this way. If there were no friction, the cars would be completely balanced and a small nudge would get them moving one way or the other. With friction, the pull of the motor is needed to overcome just the friction but not gravity. It might be easier to see what's going on if you drew separate FBDs for the two cars.
 
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