SOLUTION: The middle of a uniform 80cm long bar is placed on a knife edge and a 4kg mass is suspended from one free end of the bar. How far from the other free end must a 6.4kg mass be suspe

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Question 1149626: The middle of a uniform 80cm long bar is placed on a knife edge and a 4kg mass is suspended from one free end of the bar. How far from the other free end must a 6.4kg mass be suspended to maintain the bar horizontal position?
Answer by ikleyn(52778) About Me  (Show Source):
You can put this solution on YOUR website!
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In this simple case, the equilibrium condition states that the product of the weight by the length of the arm 
should be same for each side.


It gives the equation


    40 cm * 4 kg = x cm * 6.4 kg


From the equation,  x = %2840%2A4%29%2F6.4 = 25.


So, the mass of 6.4 kg should be suspended at 25 cm from the middle of the bar,

i.e. in  40 - 25 = 15 cm from its other end.    ANSWER

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People know this equilibrium condition just many thousand years.
Its clear mathematical formulation is attributed to Archimedes   (law of lever).

See the lesson
    - Using proportions to solve word problems in Physics
in this site.