# Homework Help: Need assistance in Physics question relevant to Torque & Static equlibrium

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1. Nov 9, 2014

### Aristotle

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

2. Relevant equations
Static equilibrium: Net force & net torque = 0

3. The attempt at a solution

Am i doing this correctly for part a?

2. Nov 9, 2014

### Jilang

Are we to assume that there are no forces on the bolts?

3. Nov 9, 2014

### SteamKing

Staff Emeritus
You are introducing an extra quantity d1 into your calculations, which will be difficult to calculate. Find an expression for sin θ based on L and H for the gantry crane as shown in the diagram.

4. Nov 9, 2014

### Aristotle

Either way even with replacing d1 with H, I still get Ft = (mgx+MgL/2) /(L sin(theta) ) . Am I on the right step?

5. Nov 9, 2014

### SteamKing

Staff Emeritus
d1 ≠ H, and the expression for sin θ is a little more complicated than that. Your expression for FT is correct.

6. Nov 9, 2014

### Aristotle

If I can't call the line of the pivot point perpendicular to the cable d1, what should I call it? I'm a little confused on what you mean. Isn't that all I'm looking for anyways: the tension in the cable as a function of the load position x? - which was the expression i found?. :/

7. Nov 9, 2014

### Jilang

Yes, it's absolutely fine. But can you express sin theta in terms of H and L ?

8. Nov 9, 2014

### Aristotle

Yes you would get sin(theta) = H/L ----> H=Lsin(theta). So then my final answer would be Ft = (mgx+MgL/2) /(L sin(theta) ) ----> Ft = (mgx+MgL/2) /(H). Much better I hope? :]

9. Nov 9, 2014

### SteamKing

Staff Emeritus
There's another triangle (which you are overlooking) which can give you an expression for sin θ. (Hint: the cable holding the support arm forms the hypotenuse of this triangle)

10. Nov 9, 2014

### Jilang

Nope. Try again.

11. Nov 9, 2014

### Aristotle

The only triangle I see is the top triangle and bottom triangle and the triangle on the left with d1.

sin theta = H/L

How else can you derive the sin theta?

12. Nov 9, 2014

### SteamKing

Staff Emeritus
sin θ is not H / L. You should review your trigonometry, especially the definitions of the sine, the cosine, and the tangent.

13. Nov 10, 2014

### Aristotle

Sorry about that, sin theta = H / sqrt (L^2 + H^2) :D