- #1
Differentiate it
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- Homework Statement
- Could someone help me out with this?
- Relevant Equations
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How does the mass of cylinder B compare to the mass of block A?
- Thread starter Differentiate it
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- Pulley pulley problem
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The discussion centers on comparing the mass of cylinder B to block A in a physics problem involving pulleys and strings. Participants emphasize the need for the original poster to share their attempts at solving the problem to receive effective help. There is a focus on defining variables related to the strings and understanding the relationships between their lengths. Questions are posed about the setup of the pulleys and their fixed positions to clarify the problem's parameters. Overall, the conversation aims to guide the original poster towards a clearer understanding of the mechanics involved.
- #2
SammyS
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Yes, someone can, but we need to see your attempt at solving this before we can begin to help.Differentiate it said:
- #3
Differentiate it
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Well I used the Net work done by a massless string thing and i seem to be getting 1.2 m/s instead of the 1.8 m/s shown in the answer keySammyS said:
- #4
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it helps to be very methodical with such questions.
Define variables for the lengths of string of interest. There's the string running from the large pulley to the rightmost pulley, the string from the centre if the large pulley to the other small pulley, the string running from the bottom of the large pulley to the bottom of that same small pulley, and the vertical string.
What fact relates those four lengths?
What fact relates the first two?
What fact relates the second and third?
Define variables for the lengths of string of interest. There's the string running from the large pulley to the rightmost pulley, the string from the centre if the large pulley to the other small pulley, the string running from the bottom of the large pulley to the bottom of that same small pulley, and the vertical string.
What fact relates those four lengths?
What fact relates the first two?
What fact relates the second and third?
- #5
SammyS
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That isn't much information regarding the specifics or your attempt. Rather than ask about how you used and obtained the Net work of the massless string, I'll ask some questions regarding the objects shown in the figure.Differentiate it said:
It looks like the two small pulleys are fixed in position relative to the bench/table. Is that correct?
Is the axel of the large pulley a fixed distance from block A ?
Is the string attached to the axel of the large pulley at one end and cylinder B at the other end?
My attempt:
Initial total M.E = PE of hanging part + PE of part of chain in the tube. I've considered the table as to be at zero of PE.
PE of hanging part = ##\frac{1}{2} \frac{m}{l}gh^{2}##.
PE of part in the tube = ##\frac{m}{l}(l - h)gh##.
Final ME = ##\frac{1}{2}\frac{m}{l}gh^{2}## + ##\frac{1}{2}\frac{m}{l}hv^{2}##.
Since Initial ME = Final ME. Therefore, ##\frac{1}{2}\frac{m}{l}hv^{2}## = ##\frac{m}{l}(l-h)gh##. Solving this gives: ## v = \sqrt{2g(l-h)}##. But the answer in the book...
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