Finding Tension in a Massless String on an Inclined Plane

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Homework Help Overview

The problem involves determining the readings of spring balances attached to blocks on a frictionless inclined plane. The scenario includes two blocks weighing 10 kg each and an incline angle of 30 degrees, with specific dimensions provided.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the tension in the string by considering the weight forces and their components. They express confusion over their calculations and the relationship between the tension and the weight of the blocks.

Discussion Status

Participants are actively discussing the calculations and interpretations of the forces involved. Some have offered guidance on checking the free body diagram and the calculations related to the components of weight. There is acknowledgment of potential errors in the original poster's approach.

Contextual Notes

The original poster has indicated uncertainty about their free body diagram and the calculations, suggesting that there may be misunderstandings about the forces acting on the blocks. The problem is framed within the constraints of a homework assignment, emphasizing the need for careful consideration of the physics involved.

toboldlygo
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Homework Statement


In the figure below, the objects are attached to spring balances calibrated in Newtons. Give the readings of the balances in each case, assuming that the strings are massless and the incline is frictionless.

04-34.gif


I need help with (d). If the picture's too grainy to read off the values, the two blocks weight 10 kg each, the angle is 30 degrees, and the sides are 5.2 m (right above the (d)) and 3 m.

Homework Equations


[/B]
F = ma, with Σ F = 0

The Attempt at a Solution


[/B]
So, I know the reading off the balance will be equivalent to the tension in the string. I've tried doing this problem two different ways: first, I found the total Weight force (98.1 N) and used the sin to find the hypotenuse, which was 196.2 N. Then, when that was wrong, I thought maybe I should use gravity, split it into components, and then multiply whatever the hypotenuse of that right triangle was by the mass. I got 196.2 N again. What am I doing wrong? I've drawn a free body diagram and everything, but I don't know what I'm doing wrong here. I have a suspicion I'm not drawing the forces correctly, but I'm not sure. Thanks in advance for any help!
 
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How can the spring balance give a value greater than the weight of the block?

Maybe show your FBD and your calcs.
 
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You determined the component of the weight parallel to the incline incorrectly.

Chet
 
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I think I figured it out. I was drawing my triangle incorrectly (the amount of silly mistakes I make when doing physics problems...). Thanks for the sanity check, paisiello2, and for hinting at what was probably wrong, chestermiller. I appreciate it!
 

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