# Finding magnitude and angle of Fnet (Concept question)

• A-linav
In summary, the conversation discusses how to find the correct angle for Fnet when using free body diagrams or addition of vectors. It is mentioned that the choice of angle to use, labeled as β, is arbitrary and can be subtracted from the given corner angle to find the correct direction on a compass. However, it is noted that in one of the provided diagrams, the angle β is not labeled, making it difficult to determine the correct angle to use. It is suggested that a diagram be included for better understanding.
A-linav

## Homework Statement

Hello,
I can find the magnitude of Fnet from free body diagrams or from addition of vectors. My issue however is how do I know when to subtract the angle I found with the corner angle? I've attached two questions and the answers to them.
In the first question, the angle that was found is the resultant angle for Fnet. In the second question, the angle that is found is then subtracted by the corner angle. How do I know what angle is the correct one for Fnet? Can someone please explain to me possibly with a diagram?

Thanks

Sine Law
Cosine Law
F=ma

A-linav said:

## Homework Statement

Hello,
I can find the magnitude of Fnet from free body diagrams or from addition of vectors. My issue however is how do I know when to subtract the angle I found with the corner angle? I've attached two questions and the answers to them.
In the first question, the angle that was found is the resultant angle for Fnet. In the second question, the angle that is found is then subtracted by the corner angle. How do I know what angle is the correct one for Fnet? Can someone please explain to me possibly with a diagram?

Thanks

View attachment 209182

Sine Law
Cosine Law
F=ma

## The Attempt at a Solution

View attachment 209183 View attachment 209184
You did not post a diagram for the second problem showing the triangle with the resultant and marking the angle β.
In each case, how to use β to find a direction in terms of the compass is evident from the diagram.

The choice of angle to call β is arbitrary.
In the diagram I drew of problem 14, it seems that to get the answer 9 degrees they subtracted the given 18 degrees from β. In the diagram for the first problem, consider what would happen if we chose to label the angle on the right as β ( the one shown as 35+45). Having computed β we would have to subtract the 45 to get the answer, making the procedure the same for both problems.

## 1. How do you find the magnitude and angle of Fnet?

To find the magnitude and angle of Fnet, you will need to use vector addition. This involves finding the x and y components of each force, adding them together, and then using trigonometry to find the magnitude and angle of the resultant vector.

## 2. What is Fnet and why is it important?

Fnet, or net force, is the sum of all the forces acting on an object. It is important because it determines the direction and magnitude of an object's acceleration, which in turn affects its motion.

## 3. How do you represent Fnet visually?

Fnet can be represented as an arrow, with the length of the arrow representing the magnitude of the force and the direction of the arrow representing the direction of the force.

## 4. Can Fnet be negative?

Yes, Fnet can be negative if the forces acting on an object are in opposite directions. In this case, the net force will be the difference between the two forces and will have a negative value.

## 5. Are there any other methods to find the magnitude and angle of Fnet?

Besides vector addition, the magnitude and angle of Fnet can also be found using the Pythagorean theorem and inverse trigonometric functions, or by using graphical methods such as scale diagrams or vector addition diagrams.

• Introductory Physics Homework Help
Replies
2
Views
760
• Introductory Physics Homework Help
Replies
14
Views
527
• Introductory Physics Homework Help
Replies
15
Views
277
• Introductory Physics Homework Help
Replies
10
Views
1K
• Introductory Physics Homework Help
Replies
9
Views
2K
• Introductory Physics Homework Help
Replies
26
Views
2K
• Introductory Physics Homework Help
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
25
Views
1K
• Introductory Physics Homework Help
Replies
17
Views
917
• Introductory Physics Homework Help
Replies
3
Views
310