A motor drives a disk initially at rest through 24.4 rotations in 5.0s. Assume the vector...

let wo = 0

let alfa is the angular acceleration when motor is switched on.

angular displacement,

theta = wo*t + (1/2)*alfa*t^2

24.4*2*pi = 0 + (1/2)*alfa*5^2

==> alfa = 24.4*2*pi*2/5^2

= 12.3 rad/s^2

angular speed of the disk bofore the motor is swirched on,

w = wo + alfa*t

= 0 + 12.3*5

= 61.5 rad/s

angular acceleration when the motor is switched off,

alfa' = (wf - w)/t

= (0 - 61.5)/12

= -5.125 rad/s^2

A) the magnitude of torque created by the force of friction, T_friction = I*|alfa'|

= 4.0*5.125

= 20.5 N.m <<<<<<<<<------------Answer

B) when the motor is switched on, Tnet = I*alfa

T_motor + T_friction = 4*12.3

T_motor - 20.5 = 49.2

T_motor = 49.2 + 20.5

= 69.7 N.m <<<<<<<<<------------Answer