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The system shown in Figure P8.20 consists of a light inextensible cord, light frictionless pulleys, and blocks of equal mass. It is initially held at rest so that the blocks are at the same height above the ground. The blocks are then released. Find the speed of block A at the moment when the vertical separation of the blocks is h. (please see the attached picture)

I used the conservation of energy and said that (KE + PE)final = (KE + PE)initial. Then i said there was no initial KE because the system was at rest and said that there was no final PE, because it had all been converted into KE. so i got the following expression:

mgh + mg(h/2) = 1/2mv^2 + 1/2m(v/2)^2

i solved for v and got sqrt(2.4gh) but this is wrong

can someone tell me where my error is??

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# Homework Help: Can someone check my work - Problem involving pulley

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