I've attached a screenshot of the question. This is what i've tried so far:(adsbygoogle = window.adsbygoogle || []).push({});

I've calculated the initial energy of the system (which is all potential energy):

Energy of disc:

0.5*I*w^2 + 0.5 *m*v^2 + m*g*h

= 0 + 0 + 0

Energy of arm:

0.5*m*v^2 + m*g*h

= 0 + 4*9.81*1.5Cos(45)

= 41.62 joules

Energy of collar:

0.5*m*v^2 + m*g*h

= 0 + 1*9.81*3Cos(45)

= 20.81 joules

Then i moved time on until the supporting arm BC was horizontal and calculated the energy at that stage (which would be all kinetic). When i do that, i end up calculating that the speed of the collar is 1.04 m/s. However, the answer is supposed to be 7.315 m/s.

I'm doing something wrong, but i can't figure out what it is. Any hints on how this is supposed to be solved would be great.

Thanks.

http://img127.imageshack.us/img127/3230/question8wo.th.jpg [Broken]

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# Constrained motion question (using moments of inertia/energy)

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