A worker lifts a 20.0-kg bucket of concrete from the ground up to the top of a 20.0-m tall building.The bucket is initially at rest,but is traveling at 4.0 m/s when it reaches the top of the building.What is the minimum amount of work that the worker did in lifting the bucket?
A) 3.92 kJ
B) 400 J
C) 560 J
D) 4.08 kJ
E) 160 J

Question

Quizplus · Accepted Answer

The work done in lifting the bucket is equal to its change in potential energy:

W = ΔU = mgh

where m is the mass of the bucket, g is the acceleration due to gravity, and h is the height the bucket was lifted.

W = (20.0 kg)(9.81 m/s^2)(20.0 m) = 3,924 J = 3.92 kJ (rounded to three significant figures).

The fact that the bucket is initially at rest but has a final velocity of 4.0 m/s at the top of the building is not relevant to the amount of work done in lifting it. The minimum amount of work done is simply determined by the change in potential energy of the bucket. Therefore, choice D is the correct answer.

A Worker Lifts a 20