A lift has a power rating of 480 W. How high can it raise two 50-kg sacks of rice in 2.0 seconds?

By the definition, power is work performed at a time unit (work divided by time). Therefore in this problem the total work done is P*T, where P is the given power and T is the given time.
Also it is known that the amount of work performed on a body adds to its total energy. The total energy of the sacks consists of the kinetic energy (m V^2)/2 and the potential energy mgh. So (mV_e^2)/2 + mgH = PT because the initial speed is probably zero. Here H is the height in question and V_e is the end speed.
To maximize H we need to minimize V_e^2, and its minimum is zero. In this case mgH = PT and H = (P T)/(mg).
Two sacks have total mass m of 100 kg. Thus the numerical answer is about (480*2)/(100*9.8) approx 1.0 m.
 
https://www.physicsclassroom.com/class/energy/Lesson-1/Power