Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

A chain 64 meters long whose mass is 20 kilograms is hanging over the edge of a tall building and does not touch the ground. How much work is required to lift the top 3 meters of the chain to the top of the building? Use that the acceleration due to gravity is 9.8 meters per second squared. Your answer must include the correct units.

share|improve this question
Hi Ryan, and welcome to Physics Stack Exchange! We don't allow homework-like questions like this where you just ask the question directly; you should narrow it down to focus on a specific physics concept first. See our FAQ and homework policy for more information. –  David Z Sep 29 '12 at 23:35
add comment

closed as too localized by David Z Sep 29 '12 at 23:34

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

3 Answers

$$ W =\int^b_a \! F \, \mathrm{d}x $$

This is the relationship between work and force, you'll need to work out what the force might be. Where a and b are the positions where you are moving from and to against the force.

If you've never done integration before $$ \int^b_a \! F \, \mathrm{d}x = [bF - aF] $$

share|improve this answer
add comment

Since the gravity is uniform and the chain is freely suspended, we just need to consider the change in height and the change in potential energy.

$$W = \Delta P.E. = mg(h_2 - h_1) $$

share|improve this answer
add comment

The density of the chain is $ \rho = \frac{20}{64} $. The amount of work is made with respect to the force $ F=mg $, but the mass is changing according how far the chain is lifted.

I think the answer is $ \rho g \int_{0}^{3}(64-x)dx $, since the work done (absolute value) is $ W= \int_{a}^{b}F.dx $

share|improve this answer
add comment

Not the answer you're looking for? Browse other questions tagged or ask your own question.