# Statics - 3 forces acting at a point -- angle α maxima

1. Aug 2, 2015

### SFG

1. The problem statement, all variables and given/known data

Please if anyone could help me with this question .

Two wires AC and BC are attached to the top of pole CD . The force exerted by the pole at C is vertical and the 2.5 kN force applied at C is horizontal and makes an angle α with the direction of the x-axis .

Find the angle α for which the tension in AC is a maximum and the corresponding tension in each cable .

as per pdf diagram

2. Relevant equations

Cos ^2 ɸx + Cos ^2 ɸy + Cos ^2 ɸz = 1

F = √Fx^2 + Fy^2 + Fz^2

Cos ɸz = Fz/F

3. The attempt at a solution

Formulate a quadratic then differentiate to get a maxima .

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2. Aug 2, 2015

### paisiello2

Try summing forces in the x-direction.

3. Aug 2, 2015

### Staff: Mentor

Which force balances do you see that you can set up?

4. Aug 2, 2015

### SFG

guys I am looking . seriously I am blanked without knowing another force or vector locations . regards SFG

5. Aug 2, 2015

### Staff: Mentor

The top of the pole is the only thing that can move, so it is useful to look at forces acting on that.
If you do not know a quantity, introduce a variable for it. That is something you will have to do frequently and everywhere.

6. Aug 2, 2015

### SFG

ok thanks guys . i'll work on this overnight . regards