Homework Help: Physics 121

Posted by Lee on Saturday, May 5, 2012 at 9:07pm.

The pulley has an inner radius of 0.35m and an outer radius of 0.65m. It has a mass of 1.8kg. A string wrapped around the inner part of the pulley is fastened to the ceiling. A second string wrapped around the outer part of the pulley is fastened to a block. Determine the mass of the block if the pulley remains at rest.

Physics 121 - Lee, Saturday, May 5, 2012 at 9:09pm
Please do show you did it and which formula did you use. Thanks very much.
Physics 121 - Elena, Sunday, May 6, 2012 at 1:51pm
The string attached to the ceiling supports the pulley and the block.
The tension of this string is T = (1.8 + m) •g,
the torque of this force is
T•r =(1.8 + m) •g•r.
The torque created by the block
is m•g•R .
The condition for equilibrium:
the net torque is zero.
(1.8 + m) •g•r = m•g•R,
m = 1.8•r/(R-r) =
= 1.8•0.35/(0.65 – 0.35) = 2.1 kg

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