Math problem????*10 pOints*?

Question

i already know the answer in #1...mY problem is #2 & #3....

1. if the power to the motor is shut off while the motor is running at 3000 rpm and a brake is applied, how much heat in joules will be dissipated in the brake in order to bring the motor to a stop?

ans. 138, 527 J (am i correct?)

2. suppose the motor has a bearing shaft diameter of 3.2 cm and the coefficient of friction of each bearing is 0.008. find the torque of friction of the bearings.

a. 0.0320 N-m

b. 0.314 N-m

c. 0.411 N-m

d. 0.481 N-m

3. referring to problem 1, suppose that, instead of the brake being applied, the motor with the power cut off is allowed to run until it is brought to a stop by the torque of friction of the bearings. how long will the armature take to come to a stop?assume all other losses (such as windage) are zero.

a. 420 sec

b. 840 sec

c. 1260 sec

d. 2810 sec

heLp me solve these pLease!!!thanks!!^_^

Answer 1

I don't think you have enough information for question 1!  Power is torque times angular speed.  We need a time or brake torque.