Mass of wheel m = 2 kg
radius of wheel r = 0.4 m
Moment of inertia of wheel I = m r ^ 2
= 0.32 kg m ^ 2
mass of disk m ' = 0.5 kg
radius of disk r ' = 0.15 m
moment of inetia of disk I ' = ( 1/ 2) m ' r ' ^ 2
= 0.005625 kg m ^ 2
(a). Initial angular speed w = 2 rev / s= 2.5 * 2π rad / s
= 15.707 rad / s
final angular speed w ' = 0
time t= 2.5 s
angular accleration α = ( w ' - w ) / t
= -6.283 rad / s ^ 2
(b). Moment of inertia of the system I " = I + I '
= 0.325625 kg m ^ 2
(c). torque of the system τ = I " α
= 2.045 N m
(d). frictional force F = τ / r
= 5.114 N