[填空题]
The blades in a blen q)lt(ky sam:*f.mpo+ der rotate at a28 -orrjw kh:lmlgs1jo (1 e*l rate of 6500 rpm. When the motor is turned off during operation, the blades slow to rest in 3.0 s. What is the angular acceleratioj8l1r1o l:sjmow-*e(kr 2gh ln as the blades slow down? $rad/s^2$