# Homework Help: Finding the Resultant Force, help needed.

1. Nov 4, 2009

### Dellis

Hi, I need some guidance regarding this exercise, I attached a visual representation of the exercise

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

Find the Resultant Force for the following system of forces shown

FORCES SHOWN on a Vector:

F1= 5 kips on the X quadrant in a 60 degree angle

F2= 5 kips straight down on the Y axis

F3= 8 kips on the X quadrant in a 30 degree angle

2. Relevant equations

These right?

Rx= $$\Sigma$$Fx= F1 + F2 + F3
Ry=$$\Sigma$$Fy= F1 + F2+ F3

(theta)Qx= Tan- Ry/Rx

3. The attempt at a solution

I want to know if I am going in the right direction, if not please guide me, this is what I tried.

Rx= $$\Sigma$$Fx= F1 + F2 + F3

=+5(sin 60 )- 5 + 8(cos 30 )

= -6.16 kips

Ry=$$\Sigma$$Fy= F1 + F2+ F3

= -5( sin 60)-5 + 8 (cos 30)

= -8.571 kips

#### Attached Files:

• ###### RESULTANT FORCES.doc
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Last edited: Nov 4, 2009
2. Nov 4, 2009

### rl.bhat

In ΣFx, there is no F2 and F1x = F1*cosθ.
In ΣFy, F1x is positive, and F3x = F3sinθ and it is negative.

3. Nov 4, 2009

### Dellis

So like this right?

Rx= $$\Sigma$$Fx= F1 + F3

=+5(cos 60 ) x 8(cos 30 )

Ry=$$\Sigma$$Fy= F1 + F2+ F3

= 5( sin 60)-5 + 8 (sin 30)

4. Nov 4, 2009

### rl.bhat

Note down whether the components are on the +ve or -ve axis.

5. Nov 4, 2009

### Dellis

This is the next steps right?

R= $$\sqrt[]{}$$ Rx+ Ry

then...

(theta)Qx= TAN-Ry/Rx

Last edited: Nov 4, 2009
6. Nov 4, 2009

### Dellis

What do you mean?, my english understanding isn't that great can you say that in another way.

I just want assurance that I am on the right path, thanks for the help btw I appreciate it.

Last edited: Nov 4, 2009
7. Nov 4, 2009

### rl.bhat

=+5(cos 60 ) x 8(cos 30 ) This step should be

=-5(cos 60 ) + 8(cos 30 )
5( sin 60)-5 + 8 (sin 30) This step should be
5( sin 60)-5 - 8 (sin 30)

8. Nov 4, 2009

### Dellis

I had it like that then got confused by your advise that said " *cos " and I took that as you saying multiply then I added an X, sorry lol.

Thanks for clearing that up, so the next steps I showed you in post#5 above is the right path correct?, that would pretty much wrap this exercise up, I will proceed once you tell me.

Last edited: Nov 4, 2009
9. Nov 4, 2009

### rl.bhat

Carry on with post5#

10. Nov 4, 2009

### Dellis

Alright thanks, I appreciate the help and guidance :)