- #1

- 29

- 0

## Homework Statement

http://imageshack.us/a/img812/8836/5tfn.jpg [Broken]

Uploaded with ImageShack.us

Find F such that the moment around A will not exceed 1000N*m for any value of θ.

## Homework Equations

M = fd

## The Attempt at a Solution

I got the right answer, I found the distance of a -> b

AB= √( (2^2) + (3^2) )

AB=3.6

and then I did

M = fd

1000 = f (3.6)

f = 277.8 N

This is correct according to the answer in the back, but I don't understand why.

1. I was under the impression for: M = fd , d must be the perpendicular distance. Clearly, the d we are using is not perpendicular to f. Does d not have to be perpendicular to the force?

2. I thought this was a trick question at first, and logically I thought it made most sense that the greatest moment around A would be caused by a force only in the vertical direction. So I tried doing it where Fx = 0 and Fy is the variable of interest.

So i tried, M = (Fy)d

1000 = (Fy)(3)

but the fy I get is clearly not the answer. Can someone explain this to me.

Last edited by a moderator: