Question

guys imma little bit confused bout this.. help

Answer 1

how come that it is cos and sin??

Answer 2

any idea?

Answer 3

u should always calculate perpendicular distances right?
u are still not comfortable with torque equations madam? .. ITS HIGH TIME.. u need proper practice!!

Answer 4

it's vectors
you can break a vector into two perpendicular components
here's an example and a tip to remember that how to do it

okay here's a vector A
it is inclined to the horizontal at an angle theta
you can break this vector into two vectors
one is horizontal (A cos theta)
and other is vertical(A sin theta)
okay
here's the tip:
if you want to break a vector into two perpendicular components, then, you can break it as follows:
the component nearer to the angle becomes the cos component and the one farther from the angle becomes the sin component
now sin and cos component means you need to multiply the sine or the cosine ratio of the angle with the vector and the angle is the inclination of the vector with the direction in and perpendicular to which you want the components of the vector.
here's one more example:

this comes from here(this is the proof)
the main vector that is broken into the components, is the resultant of the perpendicular vectors
if two vectors 'a' and 'b' are perpendicular to each other, then their resultant is given by
\[\sqrt{a^2 + b^2}\]
this comes from the formula of resultant of two vectors
and the formula is given for two vectors inclined at an angle theta (assume the vectors to be 'a' and 'b')
so the resultant R is given by the formula
R=\[\sqrt{a^2+b^2 + 2ab \cos \theta }\]
so the vectors that are in the broken form are perpendicular according to us
so theta becomes 90deg. and cos 90 =0
so the resultant becomes \[\sqrt{a^2 + b^2}\]
so if we put the values of a= Asin theta and value of b=A cos theta, we get the resultant as A
this proof is not up to the mark so please don't worry if you don't understand it
if you wanna understand it, you can search it on google :
resolution of vectors into perpendicular compponents
i hope this helps you:)
and i think now you got it why it was sine and cos