# Statics 221. Determine moment.

celtics777

## Homework Statement

Thee foot segment is subjected to the pull of the two plantarflexor muscles. Determine the moment of each force about the point of contact A on the ground.

## Homework Equations

M=Fd
I've used others to help determine certain angles, but i'm not sure if it was even necessary.

## The Attempt at a Solution

I have been able to calculate most of the angles, but i'm not exactly sure where to go from there. Which force do I use when?

Is it something like (20cos(60))(30cos(70))-(20sin(60))(30sin(70))? No idea if i'm on the right track or anything.

#### Attachments

• Statics3.jpg
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Homework Helper
Gold Member
It is often best to break up the forces ino their x and y components, then determine the moment of each component about A by using the perpendicular distance from the line of action of that component force to A, and adding them up, being sure to note signage (cw or ccw). For example, looking at the 20 N force, its x comp is 20cos60 and its y component is 20sin60. The moment from the x component is 20cos60(4).. Now find the moment from the y component of that force, and add the moments together algebraically to get the moment of that 20 N force about A. Do the same for the other force.

Edit: I'm looking at the figure bit more closely, and it is wrong. The 60 degree angle is not compatible with the dimensions shown. Toss this problem out. But remember the 'force times perpendicular distance' concept for determining moments. I'm not sure about a bad prof, but I see what you mean about a bad book (could just be a fluke, though).

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