The co-ordinates of a moving particles at a time t, are given by , $x=5 \sin 10t,y= 5 \cos 10t$. The speed of the particle is (in m/s) is

Question

$\begin{array}{1 1} (a) \;25 \\ (b) \;50\\ (c) \;10 \\ (d) \;none \end{array} $