# How much torque must the pin exert to keep the rod from rotating?

1. Mar 22, 2009

### nweis84

1. The problem statement, all variables and given/known data

How much torque must the pin exert to keep the rod from rotating?
(L=1.011m , M=3kg , m = .301kg)

So I am guessing the point of rotation is the pin??
But then how does the pin exert any torque if it is at the point of rotation?
I'm not quite sure

there is a sketch I've attached

2. Relevant equations

Ive used the equation $$\Sigma$$$$\tau$$net=0=$$\tau$$pin-$$\tau$$M-$$\tau$$m

3. The attempt at a solution
i have tried it so many ways and keep getting it wrong

$$\tau$$pin = 3kg*(1.011m/2) + .301kg*1.011m
what am i doing wrong?

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Last edited: Mar 22, 2009
2. Mar 22, 2009

### JaWiB

Re: torque

For this type of problem, you probably don't need to worry about how the pin exerts a torque (though you can imagine in reality it would take a fair amount of force since there is only a small lever arm)

It looks like you've neglected to calculate the force of each of the masses and are using the mass instead (kg*m is not the units of force)

3. Mar 22, 2009

### nweis84

Re: torque

yeah thank you i did forget to multiply by the acceleration constant g