(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I'm working through a problem:

"A particle of mass m is attached to a rod of negligible mass and length L. The rod is attached to the ground at point O. If the rod makes an angle [tex]\Theta[/tex] with the horizontal as it falls, calculate the torque about point O.

Here's a rough sketch of the diagram:

My book says that the equation for torque is [tex]\tau=Frsin\theta[/tex] where [tex]\theta[/tex] is the angle between the force and position vector.

The answer for this is [tex]Lmg cos\theta[/tex], but I don't understand why it's cosine. The book answer says to solve it in one of two ways: by multiplying the perpendicular component of the force vector to the lever arm, or by multiplying the perpendicular component of the lever arm to the force (indicating these two methods are equivilent).

How do you decide whether to use cosine or sine?

Thanks!!

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# Homework Help: A question about torque

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