Science Bowl Question

W) If the wheel is rolling smoothly, the only friction acting on it is static friction

X) When rolling down a ramp, the force of static friction on the wheel is directed down the ramp

Y) When rolling on a flat surface, the force of static friction on the wheel is directed in the opposite direction as the motion of the wheel

Z) For a wheel rolling down a ramp, the normal force is perpendicular to the ramp