- #36
TomK
- 69
- 14
Lnewqban said:Did you try a simpler problem among those before attempting solving the one we have been discussing?
This one is basically half as complex and the site shows a detailed solution:
https://i-want-to-study-engineering.org/q/pulley_dynamics_2/
It is important that you can see that both, velocity and acceleration of those pulleys, must be different and the reason behing that fact.
One (top-left) only redirects the tension of the string, while the other (bottom-right) has certain mechanical advantage (whatever it loses in force it gains in displacement and vice-verse).
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I managed to do the first pulley question, though I have a question about this second one you have mentioned.
Why do the equations of motion for masses A and B assume the acceleration direction to be down? Why does the answer come out wrong if you assume one mass goes up (for A: T - mg = maA) and the other mass goes down (for B: mg - 2T = maB)?
If you do it with 'T - mg = maA' (for mass A), you get aA = -2g/3.
If you do it with 'mg - T = maA' (for mass A), you get aA = 2g/5 (correct).
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