Power is the rate at which energy is transferred with respect to time.
When you pick a mass m from the ground up to a height h, that mass gains potential energy (U), which is given by:
[tex]U=mgh[/tex]Where g is the gravitational acceleration:
[tex]g=9.81\frac{m}{s^2}[/tex]Find the potential energy that the mass of 11.4kg gains when it is raised 0.84m:
[tex]U=(11.4\operatorname{kg})(9.81\frac{m}{s^2})(0.84m)=93.94056J[/tex]Then, divide the total potential energy by 2.3s to find the power expended in doing so:
[tex]P=\frac{U}{t}=\frac{93.94056J}{2.3s}=40.84372174\ldots W\approx41W[/tex]Therefore, the power expended to raise a mass of 11.4kg up to 0.84m above the ground in 2.3 seconds, is 41 Watts.
