Equal Moments at A: Reasoning and Calculation

NoobeAtPhysics · Nov 20, 2013

Homework Statement

Do the following have equal moments about A?

Diagram of a uniform rod of length L with pivot point A at its left end; a force F acts at the right end, directed down and to the right at 30 degrees below horizontal.

Diagram of a horizontal beam of length L with a pivot point labelled A at its left end, and a force F shown at the right end acting at 30 degrees below the horizontal, pointing down and to the left.

Homework Equations

T=rf

The Attempt at a Solution

Yes because using L*cos(30), they will be the same?

What is your reasoning?

Tanya Sharma · Nov 20, 2013

NoobeAtPhysics said:

Yes because using L*cos(30), they will be the same?

What is your reasoning?

Your reasoning is incorrect ...

τ = r×F

τ = rFsinθ

or τ = r times (component of force perpendicular to line joining A and point of application of force )

So what is τ ?

NoobeAtPhysics · Nov 20, 2013

They both use τ = rFsin30 right? That means they are equal! Right?

Tanya Sharma · Nov 20, 2013

Right...

haruspex · Nov 20, 2013

NoobeAtPhysics said:

They both use τ = rFsin30 right? That means they are equal! Right?

"Use" is a strange word there. "Supply" perhaps. Anyway, you asked whether your reasoning was correct, and Tanya S was right in reply, that your reasoning was incorrect (though you got the right answer).

Equal Moments at A: Reasoning and Calculation

Homework Statement

Homework Equations

The Attempt at a Solution

Discussion

Similar threads