Solution
1) Final speed ω3
I1=m1k12=800∗0.262=54.08kgm2
I2=m2k22=1350∗0.2252=68.34375kgm2
Conservation of energy
ω1=602πN1=602π∗300=130.8997rad/sec
ω2=602πN2=602π∗300=62.8319rad/sec (Assume the speed of the rotor was originally at 300 rpm)
I1ω1+I2ω2=(I1+I2)ω3
ω3=92.9004rad/sec=889.133rpm
2) Energy lost
K.E(before)=21∗I1∗ω12+21∗I2∗ω22=598215.06Nm
K.E(after)=21∗(I1+I2)ω32=528267.3961Nm
Lostenergy=598215.06−528267.3961=69947.66Nm
Time taken to reach the speed
T=21Wμ(R1+R2)=12906.25Nmm=12.906Nm
Angular acceleration of the rotor
I2α2=T=12.906⟹α2=0.18885rad/sec
ω3=ω2+α2t⟹t=159.22sec
Now constant resisting torque is 50Nm is applied
Torque on motor = T1=−12.906−50=−62.906Nm
ω3=ω1+α1t=ω1+I1T1t=130.8997−54.0862.906t
Considering the rotor
ω3=ω2+α2t=62.8319+0.18885t
Equating the two implies that t = 50.35 sec
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