Finding Tension in a Massless String on an Inclined Plane

AI Thread Summary
The discussion focuses on calculating the tension in a massless string on a frictionless inclined plane with two 10 kg blocks at a 30-degree angle. The user initially miscalculated the total weight force and its components, resulting in an incorrect tension reading. After guidance from other forum members, the user realized the error stemmed from incorrectly drawing the force triangle. The conversation highlights the importance of accurately representing forces in free body diagrams for solving physics problems. Ultimately, the user corrected their approach and appreciated the assistance received.
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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


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F = ma, with Σ F = 0

The Attempt at a Solution


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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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Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
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