Calculating Torque: Net Torque for 2 Forces Applied in a Plane

[cali_sk8er205]

Calculate the net torque about point for the two forces applied as in the figure below

The rod and both forces are in the plane of the page.

torque= ? Nm

http://session.masteringphysics.com/problemAsset/1026433/5/yg.10.42.jpg

is the answer -28 Nm?

i really need help I am not sure how to do problems with two forces

 

[phyzmatix]

Calculate the net torque about point for the two forces applied as in the figure below

The rod and both forces are in the plane of the page.

torque= ? Nm

http://session.masteringphysics.com/problemAsset/1026433/5/yg.10.42.jpg

is the answer -28 Nm?

i really need help I am not sure how to do problems with two forces

Remember:

$$\tau=rF_t=r_{\bot}F=rFsin\theta$$

So you have to resolve F2 into it's vertical and horizontal components for a start, then calculate the net torque and work from there.

 

[cali_sk8er205]

can you walk me through it?
ok how i think you do it is

12N*2m*sin30
-8N*5m
then add the two

sorry I am really not good at this

 

[phyzmatix]

Please don't apologise, we all know what it's like

Also, I've corrected it now, but I made a mistake in my initial post, you should calculate the torques due to both forces and then the net torque (not force like I initially mentioned, sorry about that slip).

I also notice that I edited my equation for torque, but that it never changed the equation so I'll say it again.

$$\tau=rF_t=r_{\bot}F=rFsin\theta$$

Torque can be calculated as any of the following:

In other words the torque due to $$F_2$$ can be calculated using:

$$\tau_2=rFsin\theta$$

and for $$F_1$$

$$\tau_1=rF_t$$

Finally, torque is positive when counterclockwise and negative when clockwise.

That should sort you out

Try again and let us know how far you got ok?