Why ##3.cos 60^0## is added to 4?

  • #26
The first one ......... there in my sketch ?
How many diagrams can i draw from the given question?
 
  • #27
1,522
1,384
How can you tell ##A = 4## and ##B = 3##? Why not vice versa?
You can of course change that. Whatever be your choice of A and B, you will get the angle that the resultant makes with either the 4N force, or the 3N force, depending on your choice of A and B.

For example, when you had worked out the problem, you took A=4, so you found the angle between the resultant and 4N. If you took A=3, you will find the angle between the resultant and 3N.

The mod value of the resultant remains invariant irrespective of A and B.
 
  • #28
For example, when you had worked out the problem, you took A=4, so you found the angle between the resultant and 4N. If you took A=3, you will find the angle between the resultant and 3N.
What formula should i use for finding the angle between the resultant and 4N?
 
  • #29
1,522
1,384
What formula should i use for finding the angle between the resultant and 4N?
This:
The formula is $$\phi = \tan^{-1}\left( \frac{B \sin \theta}{A+B\cos \theta}\right)$$
##\phi## is the angle that you marked as ##q##. Basically it's the angle between ##A## and the resultant.

You originally took ##\theta = 60°##, ##A = 4## and ##B = 3##, so you got the angle between 4N and the resultant. If you interchange A and B, you get the angle between 3N and the resultant.
 

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