3kW=3000 watts;
1 watt = 1 Joule/sec = Newton*metres/sec = mass*acceleration*metres/sec = volume*density*acceleration*metres/sec.
Volume of cylinder=0.750*(0.05)^2π=0.00589 cu m. Mass=8900*0.00589=267π/16=52.4253kg approx.
Change in revolution=2200-600=1600rpm=1600/60rps. Rate of change=80/(30*1.8)=400/27 revs/sec/sec.
1 rev = 2πr=0.1π=0.3142m, so rate of change (acceleration)=(400/27)*0.1π=40π/27=4.6542m/s/s.
Mass*acceleration=(267π/16)(40π/27) Newtons. Final rps=2200/60rps=110/3rps=110*0.1π m/s=11π m/s.
Energy in watts=(267π/16)(40π/27)11π=8432 watts approx = 8.432kW.
Output is 3kW, so efficiency is 3/8.432=0.36 approx or 36%.