Question

explain to me how Wx = Wsintitha instead of Wcostitha.
P= Wx + F where
F= FRICTIONAL FORCE
W= weight component along the plane(Wsintitha)
P= force applied
The topic is Work,Energy and Power in physics?

Answer 1

think of a plane lying flat on the ground (θ=0°)
the whole weight pushes down on the plane (cosθ = 1)
no weight is along the plane (sinθ = 0)

if the plane is vertical (θ=90°)
no weight (cosθ=0) pushes against the plane, since it is all pushing down along the plane (sinθ=1)

it helps to think of the extreme values to make sense of this stuff sometimes.

and that's theta, not thita