A 1.15-kg grinding wheel 22.0 cm in diameter is spinning ...

[Diane]

A 1.15-kg grinding wheel 22.0 cm in diameter is spinning counterclockwise at a rate of 20.0 revolutions per second.
 
  When the power to the grinder is turned off, the grinding wheel slows with constant angular acceleration and takes 80.0 s to come to a rest.
  (a) What was the angular acceleration (in rad/s2 ) of the grinding wheel as it came to rest if we take a counterclockwise rotation as positive?
  (b) How many revolutions did the wheel make during the time it was coming to rest?

Question 2

The angular acceleration of a wheel is given in rad/s2by 45t3  11t4, where t is in seconds. If the wheel starts from rest at t = 0.00 s, when is the next time the wheel is at rest?
 
  A) 5.1 s
  B) 8.4 s
  C) 6.9 s
  D) 3.6 s

[nital]

Answer to Question 1

(a) -1.57 rad/s2 (b) 800 revolutions

Answer to Question 2

A