- #31
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So what equation do you get by carrying out the differentiation in post #16?Adesh said:
What's my mistake in this problem in dynamics involving pulleys?
- Thread starter Adesh
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The discussion centers on finding the correct accelerations of two blocks connected by pulleys, where the initial calculations were incorrect. Block B experiences a gravitational force of 5g, but the tension in the strings must be accounted for, leading to a net force equation that includes both gravity and tension. The participants emphasize the importance of setting up force equations for each block and recognizing that the accelerations of the blocks are related due to the constraints of the string. Ultimately, the correct accelerations are derived from understanding the relationship between the lengths of the strings and the movements of the blocks. The conversation concludes with an acknowledgment of the learning gained from solving pulley problems.
- #32
Lnewqban
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Another way to look at this problem:Adesh said:
A moveable pulley can be considered as a second class lever with mechanical advantage of 2.
- #33
Adesh
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Acceleration of the blocks.haruspex said:
- #34
Adesh
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But there is something that is troubling me, ##(-l_1, 0)## is the current position of the block A and ##(0, -l_2)## is the current position of block B, but acceleration is not the second derivative of fixed positions (because in that case it will always come out to be zero). We should say, that at ##t=0## the positions of the blocks were so and so.haruspex said:
- #35
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You did not define l1 etc. as merely initial positions. Why should they not mean positions at time t, i.e. define l1 = l1(t) etc.Adesh said:
Also, you don't need to use vector representations. Just define each displacement in the direction that suits it.
- #36
Adesh
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Yes, this advice and way of solving it is helping me very much. Now, I’m able to solve almost all problems of pulleys and strings, credit goes to you.haruspex said:
I think these pulleys and strings problems are archetypical, textbooks on Newtonian Mechanics (like French’s Mechanics, Univeristy Physics) don’t actaully teach it exclusively.
Now, I’m into elevator problems
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