A motor rotates a wheel of radius (r) 0.150 meters at 85.0 rpm. If a rope around

Question

A motor rotates a wheel of radius (r) 0.150 meters at 85.0 rpm. If a rope around the wheel lifts a 115.0 kg block, the power output of the motor is  _____ watts.

A wheel whose moment of inertia is 0.350 kg/m2 is accelerated from rest to 180.0 rad/s in 5.00 seconds. When the external torque is removed, the wheel stops in 45.0 seconds. Answer the following 2 questions: The frictional torque must be ____ Nm.   The external torque must have been ____ Nm.

A motor rotates a wheel of radius (r) 0.150 meters at 85.0 rpm. If a rope around the wheel lifts a 115.0 kg block, the power output of the motor is watts. A wheel whose moment of inertia is 0.350 kg/m2 is accelerated from rest to 180.0 rad/s in 5.00 seconds. When the external torque is removed, the wheel stops in 45.0 seconds. Answer the following 2 questions: The frictional torque must be Nm. The external torque must have been Nm.

Explanation / Answer

1) Power=F*v=mg*w*r=115*9.8*85*2*pi*0.15/60=1504.7 W

2) external accn =180/5

==> external torque =I*alpha = 0.35*180/5= 12.6 N-m

frictional accn =180/45

==> frictional torque =I*alpha = 0.35*180/45= 1.4 N-m

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