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A uniform chain of total mass M and length L is suspended vertically with its lower end just touching a horizontal floor, then released from rest. Each part that hits the floor stops immediately (no rebound, no heaping). Find the total force the chain exerts on the floor at the moment a length x has piled on the floor.

1. 3Mgx/L
2. Mgx/L
3. 2Mgx/L
4. Mg(L-x)/L

Correct answer: 3Mgx/L

Solution

Two contributions: the static weight Mgx/L of the chain lying on the floor, plus the thrust 2Mgx/L from the moving links being brought to rest, totalling 3Mgx/L.

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