(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

http://img195.imageshack.us/img195/3310/exerciciospdfadobereade.png [Broken]

The uniform object AB mesures 4 meters and weighs 500N.

There is a fixed point C along which the object can rotate. The object rests on point A. A person of mass 75 kg walks over the object, starting in A.

40.1 Calculate the maximum distance x the person can walk keeping the object in equilibrium

2. Relevant equations

1)

[tex]\tau = F \times \Delta r[/tex]

2)

[tex]F = ma[/tex]

3. The attempt at a solution

I must confess beforehand that the concept of torque isnt yet confortable for me, so I'm not really sure of the following process.

first, the torque at A:

using 1)

[tex]\tau = 500 \times \Delta 2,5

= 1250[/tex] (N.m-1)

and the torque of B:

[tex]\tau = 500 \times \Delta 1,5

= 750[/tex] (N.m-1)

Now, concerning the person:

The Force applied by gravity =

[tex] 735.75 = 75 \times 9,81[/tex]

the torque of the person, then :

[tex]\tau = 735.75 \times \Delta (x-2.5)[/tex]

My guess is, when the torque of the person + torque of B = torque of A, the bar will lose equilibrium.

so :

[tex]1250 = 735.75 \times (x-2.5) + 750[/tex]

This equals aproximately 3,18 meters. However, the solution claims it to be 2.84.

What am I doing wrong?

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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# Torque and distance problem

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