- #1

zeralda21

- 119

- 1

## Homework Statement

A plank with length L is held in a place by two supports, one plank at one end A and the other a distance 5L/12 from the same end B, and is otherwise only affected by gravity. The plank has mass m. How can the vertical force on the plank be determined?

## Homework Equations

I think this: Moment=Force*Distance. Here distance is the closest from a given moment point to a force's "point of application.

## The Attempt at a Solution

I have noticed that the supports are placed at opposite sides of each other and creates a torque that are trying to rotate the plank to different directions. So in order for the plank to be at rest, the sum of the total torque must be zero.

There are two forces, a downward vertical force at A, and a upward force at B. For the plank to be in equilibrium they must be equal, or Fnet_{y}=0. Correct?

I'm not sure which moment point to choose but let it be B. Then M=A(5L/12). But it doesn't help much. And where do mg come in? i know there's a gravitational force mg but i cannot fit it in any equation.