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look416
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Homework Statement
A uniform metre rule of mass 100 g is supported by a knife-edge at the 40 cm mark and a string at the 100 cm mark. The string passes round a frictionless pulley and carries a mass of 20 g as shown in the diagram.
At which mark on the rule must a 50 g mass be suspended so that the rule balances?
Homework Equations
The Attempt at a Solution
using the [tex]\sum F[/tex]=0
therefore, R at the knife-edge + T at the 100 cm = W
R = 0.8
then take the moment at the c.g, which is at 0.5
therefore R(z)=T(50)
in the end,what i got is z=0.3125
where T=0.5N
wrong again...