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## Homework Statement

**Rigid body with one spring.**

## Homework Equations

Torque equations ( M=I * "alpha")

## The Attempt at a Solution

So I think I can solve this problem but there is only one thing I do not understand.

When I am writing my torque equation I would think that the weight of the bar and the cube would affect the torque

M = I * a + Mb * g *0.4 cos (theta) + Mw * g * 0.4 cos (theta) - k*0.4sin(theta) *0.4 cos(theta)

but apparently the equation should be

M = I*a -k*0.4sin(theta)*0.4cos(theta)

why does the mg of both the objects not affect the torque, whenever I try to include them the differential equation becomes unsolveable