vectors physics

Question

need solution for 21st and 22nd question

Comments

Please upload clear image for question 21st and 22nd

Answer 1

need solution for 11th question

(N-1) identical forces act simultaneously on a particle each making an angle of 360/N with the preceding one, the resultant is

Comments

From the question 11th, For N=1(plus or minus) , the magnitude of force vector will be F and direction is the vector itself.
For any other N , the answer will be 0
So, the resultant vector will be 0 if it is pointing to the vertices of a symmetric and closed figure

Answer 2

From the question 11th, For N=1(plus or minus) , the magnitude of force vector will be F and direction is the vector itself. 
For any other N , the answer will be 0 
Explanation: 
put N=2 
You get vectors 180 deg. apart , which will cancel each other out( like on positive x axis and negative x axis) 
Put N=3 
You get vectors which are 120 deg apart, looks something like this ( only see the figure on that page) 

But vectors can be displaced , so can also displace it to make a triangle (equilateral triangle) , by doing so you will realize that , by walking along the vector you will end up on same position from where you have started. Which means net vector is 0 . 
This theorem is true for all closed shapes like triangle , square, pentagon , hexagon etc. 

For N=4 
Vector points towards the vertices of square 
For N=5 
Vector points towards the vertices of pentagon 
Than 
Hexagon ...........so on 

Hence the resultant vector will be 0 if it is pointing to the vertices of a symmetric and closed figure