If both the projection Pa and component Fb of the force F are 305 N, determine the magnitude F and the orientation è of the b-axis.

The angle between the negative y axis and the a- axis is 70 degrees.

The angle between the negative y axis and the force F is 108 degrees.

I found the Force F=305/cos38 = 387.05, but am having trouble with the angles. The answer requires a positive and negative angle theta.

1 answer

The angles are not precisely specified.
It is not clear whether the a-axis makes an angle of -20 (340) with the x-axis, or -160 (200) with the x-axis.
Same problem for the force F.

Could you specify forces and axes using the following conventions:
1. All angles are measured from the positive x-axis.
2. Angles measured counterclockwise (CCW) are positive, angles measured clockwise (CW) are negative.
3. All forces (and axes) originate from the origin. Forces towards the origin may be converted to originate therefrom by adding 180 degrees.

After that, draw a diagram and make a table. Unknown quantities (force or orientation) should be denoted by a variable name.