- #1

paul11

- 7

- 0

## Homework Statement

A uniform plank of length 5.0 m and weight 212 N rests horizontally on two supports, with d = 1.41 m of the plank hanging over the right support. To what distance, x, can a person who weighs 433 N walk on the overhanging part of the plank before it just begins to tip?

## Homework Equations

Tnet = 0

T = r * F

## The Attempt at a Solution

I already found the answer, but there's something that bugs me.

Torque of plank = Torque of person

212N * 1.09m = 433N * distance

The right support is the fulcrum point.

What I don't understand is why the plank's weight acts on is 1.09m. I know the idea to get the midpoint from the two supports then subtract by the plank that is hanging over the right support, 5.00m / 2 - 1.41m = 1.09m, but I don't understand why this is the case.

This is what I initially did, 5.00m + 1.41m = 6.41m, then I divided this value by 2 to get 3.205m, and this is the center point of the plank from either end point. This point will be 1.795m from the right support, and I used this to calculate the torque of the plank. Could someone enlighten me why this was wrong? And why the correct way is .. correct?