- #1

- 7

- 0

## Homework Statement

The diagram shows a uniform plank of length 5m and weight 225N that rests horizontally on two supports, with 1.1 m hanging over the right support. To what distance x can a person who weighs 450 N walk on the overhanging part of the plank before it just begins to tip?

l-x-l

\0/

l

/\

_________________

^ ^

l-1.1m-l

## Homework Equations

T=Fl

[tex]\Sigma[/tex] T = 0

[tex]\Sigma[/tex] F = 0

## The Attempt at a Solution

Take upward direction as positive and clockwise direction of motion as positive

Name the leftmost fulcrum L and the right fulcrum R

Fy = F

_{L}+ F

_{R}- F

_{Wplank}- F

_{WPerson}

Fy = 0

Thus F

_{L}+ F

_{R}- 225N - 450 N = 0

Thus F

_{L}= 675N - + F

_{R}

This is where I get stuck. My equation kept boiling down to rubbish and when I checked the web for a solution, I found out I need to make the torque produced by Force L a negative number with respect to fulcrum R. However, won't the upward force of L produce a clockwise rotation? The rotation at R caused by force L is the only place that I seem to be messing up as other equations are exactly as the memo indicated. But I have taken clockwise to be positive (as the memo also indicated) and yet the memo says that my torque at L is negative.