Answer
$\overline P=2.43\times10^4W$
Work Step by Step
We assume the lifting force $L$ is a nonconservative force. According to the work-energy theorem, $$W_{nc}=E_f-E_0$$ $$W_L=\frac{1}{2}m(v_f^2-v_0^2)+mg(h_f-h_0)$$
We know $v_0=0$, $v_f=7m/s$, $m=810kg$ and $h_f-h_0=8.2m$. Therefore, $$W_L=8.49\times10^4J$$
The average power generated by the lifting force is $$\overline P=\frac{W_L}{t}=2.43\times10^4W$$
