# Homework Help: Basic Statics Mechanics - moments

1. Sep 8, 2007

I think I am getting the wrong answer here, but I don't know why. Would someone please be so kind to go through this basic stuff.

Question: The force F exerts a 200 ft-lb counterclockwise moment about A and a 100 ft-lb clockwise moment about B. What are F and theta?

Attempt:
$$M_A = 2 F \cos \theta + 9 F \sin \theta = 200$$
$$M_B = -7 F \cos \theta + F \sin \theta = -100$$

A little bit of algebra yields:
$$\frac{\sin \theta}{\cos \theta} = \frac{12}{-11}$$

$$\tan \theta = \frac{12}{-11} = -47.49 (deg)$$

Would someone please tell me what I am doing wrong. Thanks!

2. Sep 8, 2007

### PhanthomJay

You missed a minus sign somewhere, tan theta = +12/11; otherwise, your work looks good to me, theta = +47.5 degrees, (and F = 25 pounds).
(there is a typo in the figure at joint A, I think: should read (-5,5))