First of all im sorry for my awful english. 1. The problem statement, all variables and given/known data Electric motor starts turning wheel with a constant power of P=25W and J=3 kg*m^2. With what angular velocity the wheel spins after 7s(from start), if the efficiency is 60% 2. Relevant equations P=M*ω M=J*α 3. The attempt at a solution Ok so i have equasion that gives correct number(solution) for this particular case, but i wanna to know how did guy that wrote it came up with it and if its correct anyway. so, equasion is: ω=sqrt((2*P*t)/J)=10,80 rad/s. Correct answer is ω≈8.4 rad/s (100% correct its from our exam) I tried to get to this equasion by myself so i did this: ω=P/M=P/(J*α)=P*t/(J*ω) so ω^2=P*t/J ω=sqrt(P*t/J) The other thing that bothers me is that efficiency is not iven used. So any help how to develop correct equasion would be nice.