The boy lifted a bucket of water weighing 8 kg from a well 10 m deep in 30 seconds.

The boy lifted a bucket of water weighing 8 kg from a well 10 m deep in 30 seconds. What work did the boy do? How much power has he developed?

The work expended is equal to the power multiplied by the time, that is.
Az = P * t
According to the law of conservation of energy, this work is equal to the potential energy of the bucket:
P * t = mgh.
First, let’s answer the first question by finding Az as Az = mgh = 800J.
Let’s answer the second question.
P * t = mgh
P = mgh / t = 800/30 = 26.7W