# Calculating moments of forces/fulcrum PDF file attached

1. Sep 13, 2011

### mt05

1) see pdf
for question 2 i'm unsure how to calculate the force at the fulcrum since its not in equilibrium. I thought maybe i would add the two forces together, but that doesn't seem right.

2) so this question asks for what forces need to be applied at points A and B and i understand what forces need to be applied at A ( i think ). but at point B wouldn't the fulcrum have to have an equal amount of force pushing up...so 50+20 = 70N...doesn't seem right since the fulcrum isn't centered.

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Last edited: Sep 13, 2011
2. Sep 14, 2011

### kuruman

For question 2
The statement of the problem is missing, so I assume that the mass of the bar is given. Call it m. You need to write two expressions for Newton's Second Law, ∑F = macm and ∑τ = Ifulcrumα. Here Ifulcrum is the moment of inertia of the bar about the fulcrum.

For question 3, is there friction at the fulcrum? If no, then it seems that you have put in the right forces. It is assumed that the fulcrum provides whatever force is necessary to keep the bar at equilibrium.

*** On edit ***
Are we to assume that gravity acts on this bar?

Last edited: Sep 14, 2011