Acceleration is -10.57 rad/s² Â
Time is 6 seconds
u=900rpm= 94.248 rad/s Â
v =300rpm= 31.416 rad/s Â
s=60 revolutions= 377 rad Â
v²= u²+ 2as Â
31.416² = 94.248²+ 2 * a * 377 Â
a = v²-u² / 2s
a= -10.57 rad/s² Â
Using 1st equation of motion
v-u/a = t
Putting the values
t = (31.4 - 94.2)/-10.57
t = 6 seconds