What equations can I use to find missing values in a 3D vector problem?

[DaVinci]

Im stuck on a 3d vector problem. I know Fx and Fz and angle Beta. I've looked at all the equations in the book (both my statics and physics book) and just cannot seem to put the given data together in a manner to give me another value. If I can just get either Fy or one of the other angles, I can work the rest out.

Can someone give me a hint as to what to use to find Fy, alpha, gamma, or F when given Fx, Fz, and beta?

For your own reference, the problem is:

The pole is subjected to the force F which has components Fx = 1.5kN and Fz = 1.25kN. If Beta = 75 degrees, determine the magnitudes of F and Fy.

If I can get one more value, I can use the direction cosines and get the other angles. If I knew F, I could determine Fy. I just can't get another value.

Any hints would be appreciated.

 

[vincentchan]

what is beta? what is alpha? what is gamma? how do you define it?

just let you know, we don't have the same textbook you have, and don't go to class with you. if you don't tell us more specific how do you define your variable, no one could answer you...

 

[DaVinci]

Oh, I thought is was convention that alpha is the angle between the x-axis and the vector, beta is the angle between the y-axis and the vector, and gamma is the angle between the z-axis and the vector.

So much for standardization amongst science.

Will remember that for the future.

 

[DaVinci]

Few hours later and this one is still driving me nuts.

I tried to take the F vector projections on each plane and came up with 3 equations there and used the cosine^2alpha + cos^2beta + cos^2gamma = 1 equation and solve but the numbers don't come out right.

 

[DaVinci]

And after those few hours it comes down to a stupid arithmitic mistake...

--slap forhead--

Got it soved.