A 10 m chain with total mass of 80 kg is laid out on the ground. How much work is required to lift one end of the chain 6 m off the ground?
This is a standard problem from a standard textbook, in the requisite section on work.
Before we solve the problem, we need to draw a picture. So I asked my students to do that the other night.
Can you see the tension?
So. Who’s right?
Surely you object that things would be different if my chain actually weighed 80 kg. Perhaps you are right. Perhaps they would be different.
But here’s the thing…
My 10 ft of chain is a bit more than half a kilogram. So 10 meters of this chain is less than 2 kg. So the chain in the problem is 40 times more massive than the one from my local hardware store. How big is this chain anyway?