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A uniform chain of $$6$$ m length is placed on a table such that a part of its length is hanging over the edge of the table. The system is at rest. The co-efficient of static friction between the chain and the surface of the table is $$0.5$$, the maximum length of the chain hanging from the table is ______ m.
Correct Answer: 2
Let the total length of the chain be $$L = 6$$ m and the coefficient of static friction be $$\mu = 0.5$$.
Let $$x$$ be the length of the chain hanging over the edge. Then $$(L - x) = (6 - x)$$ is the length on the table.
Let the mass per unit length of the chain be $$\lambda = \frac{m}{L}$$.
Weight of the hanging part (pulling the chain down):
$$W_{hang} = \lambda x g = \frac{m x g}{6}$$
Normal force on the table part:
$$N = \lambda (6 - x) g = \frac{m(6 - x)g}{6}$$
Maximum static friction force:
$$f = \mu N = 0.5 \times \frac{m(6 - x)g}{6}$$
At the maximum hanging length, the system is on the verge of sliding, so:
$$W_{hang} = f$$
$$\frac{m x g}{6} = 0.5 \times \frac{m(6 - x)g}{6}$$
Cancelling common terms:
$$x = 0.5(6 - x)$$
$$x = 3 - 0.5x$$
$$1.5x = 3$$
$$x = 2 \text{ m}$$
The maximum length of the chain hanging from the table is 2 m.
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