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

A plank, of length L = 3.7 m and mass M = 7.0 kg, rests on the ground and on a frictionless roller at the top of a wall of height h = 1.70 m (see the figure). The center of gravity of the plank is at its center. The plank remains in equilibrium for any value of θ >= 74° but slips if θ < 74°. Calculate the magnitude in newtons of the force exerted by the roller on the plank when θ = 74°.

I got this part, the force is 19.8N

Continuation: Calculate the magnitude in newtons of the normal force exerted by ground on the plank when θ = 74°.

I get stuck here.

2. Relevant equations

T=Ia

3. The attempt at a solution

I calculated the torque down that goes thrugh the center of mass of the plank.( the center of mass is just above the corner of the ledge that the plank is leaning on)

I also calculated the torque that the edge of the wall exerts on the board in the opposite direction.

If I set the point where it contacts the ground as the pivot point, I get

T(of COM) - t(of wall) = 0

The only problem that the above is not true. I know that I am missing something but I am not sure what it is.

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# Homework Help: Calculate the magnitude in newtons of the normal force

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