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## Homework Statement

The 20-cm-diameter disk in the figure can rotate on an axle through its center.

What is the net torque about the axle?

image: http://session.masteringphysics.com/problemAsset/1000963/5/knight_Figure_13_14.jpg

## Homework Equations

τ=Frsinφ

## The Attempt at a Solution

τnet= τ1+τ2+τ3+τ4

τ1 = 30N * 0.1 * sin(90)

τ2 = 30N * 0.05 * sin(-45)

τ3 = 20N * 0.05 * sin(-90)

τ4 = 20N * 0.1 * sin(45)

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τnet =~2.35355 Nm

this was my original solution, which came out incorrect, a friend then told me that τ4 is zero because the force of 20N is not being applied to a point on the disk itself, so then:

τ1 = 30N * 0.1 * sin(90)

τ2 = 30N * 0.05 * sin(-45)

τ3 = 20N * 0.05 * sin(-90)

_____________________

τnet =~0.94 Nm

the issue is that I have only one attempt left at this problem and I want to confirm this before I submit the problem