Homework Help: Sum of Torque and Forces

1. Nov 19, 2006

Soaring Crane

A light triangular plate OAB is in a horizontal plane. The 3 forces, F1 = 7 N, F2 = 3 N, F3 = 8 B, act on the plate, which is pivoted about a vertical axes through point O. Consider the counterclockwise sense as positive. The sum of the torques about the vertical axis through point O, acting on the plate due to forces F1, F2, and F3, is closest to:

a. 0.30 N*m-----------b. 1.2 N*m---------c. –0.30 N*m------d. –1.2 N*m-------e. zero

In the attachment, please note that the angle between F1 and the dotted line is 30 degrees. The angle between the dotted line and F3 is 45 degrees.
Angle 1 = 30 degrees
Angle 3 = 45 degrees

Hypotenuse = 1.0 m

If you cannot see the attachment, please tell me.

Since the plate is rotated around point O,

The torque where F3 acts is 0 m*N since r = 0 m??

Therefore, only forces 1 and 2 are left.

Is Force 2 counterclockwise, which makes it positive? Torque 2 = F*r*sin theta = 3N*0.8 m*sin 90 = +2.4 m*N??

Is Force 1 clockwise, which makes it negative? Torque 1 = F*r*sin theta = 7N*sin 90*0.6 m = -2.1 m*N?

Sum of torques = 2.4 m*N – 2.1 m*N = 0.30 m*N??

Thanks.

Attached Files:

• Triangularplate2.bmp
File size:
58.8 KB
Views:
435
2. Nov 19, 2006

Unfortunately, I cannot see the attachment, but it is possibly due to my computer [:grumpy:]. But yes, if the force vector intersects with the axis, the torque produced by that force must equal zero.

3. Nov 19, 2006

Soaring Crane

I tried saving it as a Word document. Hopefully, it is accessible now.

Attached Files:

• Diagramplate.doc
File size:
71 KB
Views:
311
4. Nov 20, 2006

Soaring Crane

Are my signs for the torque correct?

Thanks again.

5. Nov 21, 2006