[填空题]
The blades in a blen /r, toj0n9kavkjo-9bder rotbqlp5q,g;,xs cjm-2 sate at a rate of 6500 rpm. When the motor is turned off during operation, the bladescqb ms5j- ,sg;p2,qlx slow to rest in 3.0 s. What is the angular acceleration as the blades slow down? $rad/s^2$