A constant horizontal force of magnitude 10 N is applied to wheel of mass 10 kg and radius 0.30 m (Figure). The wheel rolls smoothly on the horizontal surface, and the acceleration of its center of mass has magnitude 0.60 m/s2. (a) What are the magnitude and direction of the frictional force on the wheel? (b) What is the rolling inertia of the wheel about the rotation axis through its center of mass? Solution http://panda.unm.edu/Courses/Price/Phys160/p25-2.pdf I understand part a but i have a question on part b. I know that τ = r x f so why, in this problem, τ = (.3m)(4N)? why is only friction force calculated and not the force applied to it which was 10N?