Velocity would be the derivative of position, so differentiate.
The position ( in feet) of an object oscillating up and down at the end of a spring is given by s = A sin [ (square root of ( k/m)) * t ]
at time t ( in seconds). The value of A is the amplitude of the motion, k is a measure of the stiffness of the spring, and m is the mass of the object. Find the object's velocity at time t.