energy, work!!!!?

Question

a worker on a building site raises a bucket full of cement at a slow steady speed, using a pulley. the weight of the bucket is 200 N. the force which worker produces is 210 N. the bucket is raised through a height of 4m.
-through what distance does the worker pull the rope?
-how much work is done on the bucket and cement?
-how much work is done by the worker?
-where does the energy used by the worker come from?

Answer 1

Since the bucket rises at a slow, steady speed, the pulley must have a coefficient of friction of 10/210 = 0.0476.
the force exerted on the bucket is 200 N and it rises 4 m, so the work done on the bucket is
W = 800 J

The worker exerts a force of 210 N through 4 m, or
W = 840 J

The energy used by the worker probably came from Burger King, although McDonalds is a fair 2nd choice.

Answer 2

Because your question involves using one of the recognized 5-simple machines, the mechanical advantage of the pulley needs to be considered in any calculations. A machine is a device used for the multiplying forces or changing their direction. In almost all instances most machines multiply forces by increasing a distance.

Every simple machine pulley system needs to be considered on its advantage ratio. If you were using a pully system called a block and tackle that had a 10:1 ratio you could lift 500 newtons with only 50newtons of pull. At 10:1 you would need to pull out 10 meters of rope for every 1 meter you wanted to rise the mass.

In your problem the guy is exerting more force that the bucket has, and there is a loss rather a gain. This guy is working harder to lift the bucket with the pulley so he must not be using a simple machine even though a pulley is present.

If the bucket is raised 4-meters, it would appear that 4-m of rope was used and that distance of rope needed to be displaced in order to move the bucket a distance of 4-meters.

The amount of work done on the bucket can be calculated Force x Distance = 800J

The amount of work performed BY the worker is Force x Distance = 840J.

We will assume the the energy used by the worker came from his muscles which were fueled by the the human bio-metobolism of the the Big Mac sandwhich he ate for lunch that day.