Let at any instant of time the speed is vo and the angle made by the bike with the horizontal is given
now we have
component of speed in x direction given as
[tex]v_x = v_0cos\theta[/tex]
component of speed in y direction will be
[tex]v_y = v_0sin\theta[/tex]
now from above two equations we can say that here
[tex]\theta[/tex] = angle with the horizontal at any instant
and since here it is a sine curve so we know that
[tex]y = sin(x)[/tex]
so we have slope of graph
[tex]tan\theta = \frac{dy}{dx} = cos(x)[/tex]
