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21joanna12
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Homework Statement
) The pulley system in Figure 1.b consists of two pulleys of radii a and b rigidly fixed
together, but free to rotate about a common horizontal axis. The weight W hangs
from the axle of a freely suspended pulley P, which can rotate about its axle. If
section A of a rough rope is pulled down with velocity V :
(i) Explain which way W will move.
(ii) With what speed will it move?
THE IMAGE IS IN QUESTION 3 HERE: http://www.physics.ox.ac.uk/olympiad/Downloads/PastPapers/BPhO_Round_1_2013_prt_1.pdf
Homework Equations
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The Attempt at a Solution
The answer is that the weight will move up because rope B moves down with velocity (b/a)V and D moves up with velocity V, so the centre of the weight rises with speed V(a-b)/2a
I really can't see why the mass would move up. Surely the same amount of string is fed through to each side of the pulley so it should not move?
Thank you in advance!