How can I know which law of force should be use to calculate....

[Benjamin_harsh]

Homework Statement

How can I know which law of force should be use to calculate magnitude and direction for any diagram?

Relevant Equations

Triangle law of forces

for this diagram, I want to use Triangle law of forces, but I am not sure about final answer.
So how can I know which law of force should be use to calculate magnitude and direction for any diagram?

 

[Doc Al]

What are you trying to calculate? If you want to sum those forces, there are several ways to do so. Realize that you can move the force vectors around so that they can be added as a triangle.

 

[Benjamin_harsh]

What are you trying to calculate?

I want to calculate magnitude and direction.

 

[Doc Al]

Of the sum, I presume. Try moving the 150 force so its tail hits the tip of the other vector. You can translate vectors as long as you don't change their directions.

 

[Gaussian97]

Problem Statement: How can I know which law of force should be use to calculate magnitude and direction for any diagram?
Relevant Equations: Triangle law of forces

View attachment 243841
for this diagram, I want to use Triangle law of forces, but I am not sure about final answer.
So how can I know which law of force should be use to calculate magnitude and direction for any diagram?

What are the different "laws of force" that you know?

 

[Benjamin_harsh]

What are the different "laws of force" that you know?

Only 2 I know.

Parallelogram law of force.

Triangular law of force.

 

[Doc Al]

I presume that by "triangular law of force" you mean the "head to tail" method of vector addition? That way they form a triangle, which you can then use to find the resultant.

 

[Benjamin_harsh]

I presume that by "triangular law of force" you mean the "head to tail" method of vector addition? That way they form a triangle, which you can then use to find the resultant.

So parallelogram law of force is useless for this problem?

 

[Doc Al]

So parallelogram law of force is useless for this problem?

Not sure what the "parallelogram law" is, but you can use ANY method to add the two vectors.

 

[Benjamin_harsh]

Not sure what the "parallelogram law" is, but you can use ANY method to add the two vectors.

I am saying Parallelogram law of vector addition

 

[Doc Al]

Ah, you mean this:

Nothing wrong with that. (To me, those are sort of the same thing: Graphical methods of adding vectors.)

The real trick is to move the vectors so that they are head to tail.

 

[Gaussian97]

I presume that by "triangular law of force" you mean the "head to tail" method of vector addition? That way they form a triangle, which you can then use to find the resultant.

I think that "triangular law of force" means the cosine rule.

Only 2 I know.

Parallelogram law of force.

Triangular law of force.

You can always use the parallelogram law, but it's a geometric proceeding so you will need a ruler to measure the final result and you will have errors. Triangular law of force, if I understand what you mean (please explain what do you understand by this) can be used also to get the correct values with mathematical operations.

 

[Doc Al]

I think that "triangular law of force" means the cosine rule.

Yep. And I'd use that rule even for the parallelogram method (there's a triangle in there) so you can get an exact answer.

(In reality, I wouldn't waste time with either: I'd just add components.)