Find the angle formed by two forces of 7n and 15n respectively if its result is worth 20n

First, you need to make certain assumptions before solving this question. Why? Because there are no information given about the direction of these forces. In such questions as above, ALWAYS make the following assumptions:

1) Take first force, say , and assume that it is pointing towards the x-direction.

Let us take the 7N force! By keeping the above assumption in our minds, the force vector would be like:
= , where = Unit vector in the x-direction.

2) Take the second force, say , and assume that it is making an angle  with the first force .

Let us take the 15N force! By keeping the above assumption in our minds, the forces vector would be like:



Now from simple vector addition, we know that,
--- (A)

Where = Resultant vector.
NOTE: In equation (A), all forces are in vector notation. Assume that there is an arrow head on top of them.

Let us find first!
 =  

=>  =  

Now the magnitude of  is,
| | = 

=> | | = 

Since , therefore,

=> | | = 

Since  | | = ||, and the magnitude of the resultant force is 20N, therefore,

 || = | |
20 =

Take square on both sides,
400 =




Ans: Angle formed by the two forces, 7N and 15N, is: 53.13°

-israr

One splits the atoms and molecules  the other combines them

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.